Adding AMK's guide (merge)

doc/guide/Makefile

+
+PYTHONSRC=$$HOME/projects/python
+
+TEX_FILES = gfdl.tex introduction.tex  modules.tex  prog-zodb.tex  \
+            storages.tex  transactions.tex  zeo.tex  zodb.tex 
+
+MKHOWTO=$(PYTHONSRC)/Doc/tools/mkhowto
+
+zodb.dvi: $(TEX_FILES)
+	$(MKHOWTO) --dvi zodb.tex
+
+html:
+	-rm -rf zodb
+	$(MKHOWTO) --html --iconserver=/python/writing/icons zodb.tex
+#	rm -f /home/amk/www/zodb/guide/*
+#	cp -p zodb/* /home/amk/www/zodb/guide/
+
+
+

doc/guide/README

+This directory contains Andrew Kuchling's programmers guide to ZODB
+and ZEO.  It is taken from Andrew's zodb.sf.net project on
+SourceForge.  The SF version should be considered the canonical
+version, so don't make edits here for now.
+
+Eventually, we'll finish merging the two projects and then the version
+here will be the canonical one.  For now, we have to manually keep the
+two directories in sync.

doc/guide/TODO

+Update text to use BTrees, not BTree
+Write section on __setstate__
+Connection.sync seems to work now; note this
+Continue working on it
+Suppress the full GFDL text in the PDF/PS versions
+

doc/guide/admin.tex

+
+%  Administration
+%    Importing and exporting data
+%    Disaster recovery/avoidance
+%    Security
+

doc/guide/chatter.py

+
+import sys, time, os, random
+
+from ZEO import ClientStorage
+import ZODB
+from ZODB.POSException import ConflictError
+from Persistence import Persistent
+import BTree
+
+class ChatSession(Persistent):
+
+    """Class for a chat session.
+    Messages are stored in a B-tree, indexed by the time the message
+    was created.  (Eventually we'd want to throw messages out,
+
+    add_message(message) -- add a message to the channel
+    new_messages()       -- return new messages since the last call to
+                            this method
+    
+    
+    """
+
+    def __init__(self, name):
+        """Initialize new chat session.
+        name -- the channel's name
+        """
+
+        self.name = name
+
+        # Internal attribute: _messages holds all the chat messages.        
+        self._messages = BTree.BTree()
+        
+
+    def new_messages(self):
+        "Return new messages."
+
+        # self._v_last_time is the time of the most recent message
+        # returned to the user of this class. 
+        if not hasattr(self, '_v_last_time'):
+            self._v_last_time = 0
+
+        new = []
+        T = self._v_last_time
+
+        for T2, message in self._messages.items():
+            if T2 > T:
+                new.append( message )
+                self._v_last_time = T2
+
+        return new
+    
+    def add_message(self, message):
+        """Add a message to the channel.
+        message -- text of the message to be added
+        """
+
+        while 1:
+            try:
+                now = time.time()
+                self._messages[ now ] = message
+                get_transaction().commit()
+            except ConflictError:
+                # Conflict occurred; this process should pause and
+                # wait for a little bit, then try again.
+                time.sleep(.2)
+                pass
+            else:
+                # No ConflictError exception raised, so break
+                # out of the enclosing while loop.
+                break
+        # end while
+
+def get_chat_session(conn, channelname):
+    """Return the chat session for a given channel, creating the session
+    if required."""
+
+    # We'll keep a B-tree of sessions, mapping channel names to
+    # session objects.  The B-tree is stored at the ZODB's root under
+    # the key 'chat_sessions'.
+    root = conn.root()
+    if not root.has_key('chat_sessions'):
+        print 'Creating chat_sessions B-tree'
+        root['chat_sessions'] = BTree.BTree()
+        get_transaction().commit()
+        
+    sessions = root['chat_sessions']
+
+    # Get a session object corresponding to the channel name, creating
+    # it if necessary.
+    if not sessions.has_key( channelname ):
+        print 'Creating new session:', channelname
+        sessions[ channelname ] = ChatSession(channelname)
+        get_transaction().commit()
+
+    session = sessions[ channelname ]
+    return session
+    
+
+if __name__ == '__main__':
+    if len(sys.argv) != 2:
+        print 'Usage: %s <channelname>' % sys.argv[0]
+        sys.exit(0)
+
+    storage = ClientStorage.ClientStorage( ('localhost', 9672) )
+    db = ZODB.DB( storage )
+    conn = db.open()
+
+    s = session = get_chat_session(conn, sys.argv[1])
+
+    messages = ['Hi.', 'Hello', 'Me too', "I'M 3L33T!!!!"]
+
+    while 1:
+        # Send a random message
+        msg = random.choice(messages)
+        session.add_message( '%s: pid %i' % (msg,os.getpid() ))
+
+        # Display new messages
+        for msg in session.new_messages():
+            print msg
+
+        # Wait for a few seconds
+        pause = random.randint( 1, 4 ) 
+        time.sleep( pause )
+        

doc/guide/gfdl.tex

+% gfdl.tex 
+% This file is a chapter.  It must be included in a larger document to work
+% properly.
+
+\section{GNU Free Documentation License}
+
+Version 1.1, March 2000\\
+
+ Copyright $\copyright$ 2000  Free Software Foundation, Inc.\\
+     59 Temple Place, Suite 330, Boston, MA  02111-1307  USA\\
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+

doc/guide/indexing.tex

+
+% Indexing Data
+%    BTrees
+%    Full-text indexing
+

doc/guide/introduction.tex

+
+%Introduction
+%   What is ZODB?
+%   What is ZEO?
+%   OODBs vs. Relational DBs
+%   Other OODBs
+
+\section{Introduction}
+
+This guide explains how to write Python programs that use the Z Object
+Database (ZODB) and Zope Enterprise Objects (ZEO).  The latest version
+of the guide is always available at
+\url{http://www.amk.ca/zodb/guide/}.
+
+\subsection{What is the ZODB?}
+
+The ZODB is a persistence system for Python objects.  Persistent
+programming languages provide facilities that automatically write
+objects to disk and read them in again when they're required by a
+running program.  By installing the ZODB, you add such facilities to
+Python.
+
+It's certainly possible to build your own system for making Python
+objects persistent.  The usual starting points are the \module{pickle}
+module, for converting objects into a string representation, and
+various database modules, such as the \module{gdbm} or \module{bsddb}
+modules, that provide ways to write strings to disk and read them
+back.  It's straightforward to combine the \module{pickle} module and
+a database module to store and retrieve objects, and in fact the
+\module{shelve} module, included in Python's standard library, does
+this.
+
+The downside is that the programmer has to explicitly manage objects,
+reading an object when it's needed and writing it out to disk when the
+object is no longer required.  The ZODB manages objects for you,
+keeping them in a cache and writing them out if they haven't been 
+accessed in a while.  
+
+
+\subsection{OODBs vs. Relational DBs}
+
+Another way to look at it is that the ZODB is a Python-specific
+object-oriented database (OODB).  Commercial object databases for C++
+or Java often require that you jump through some hoops, such as using
+a special preprocessor or avoiding certain data types.  As we'll see,
+the ZODB has some hoops of its own to jump through, but in comparison
+the naturalness of the ZODB is astonishing.
+
+Relational databases (RDBs) are far more common than OODBs.
+Relational databases store information in tables; a table consists of
+any number of rows, each row containing several columns of
+information.  (Rows are more formally called relations, which is where
+the term ``relational database'' originates.)
+
+Let's look at a concrete example.  The example comes from my day job
+working for the MEMS Exchange, in a greatly simplified version.  The
+job is to track process runs, which are lists of manufacturing steps
+to be performed in a semiconductor fab.  A run is owned by a
+particular user, and has a name and assigned ID number.  Runs consist
+of a number of operations; an operation is a single step to be
+performed, such as depositing something on a wafer or etching
+something off it.
+
+Operations may have parameters, which are additional information
+required to perform an operation.  For example, if you're depositing
+something on a wafer, you need to know two things: 1) what you're
+depositing, and 2) how much should be deposited.  You might deposit
+100 microns of silicon oxide, or 1 micron of copper.
+
+Mapping these structures to a relational database is straightforward:
+
+\begin{verbatim}
+CREATE TABLE runs (
+  int      run_id,
+  varchar  owner,
+  varchar  title,
+  int      acct_num,
+  primary key(run_id)
+);
+
+CREATE TABLE operations (
+  int      run_id,
+  int      step_num, 
+  varchar  process_id,
+  PRIMARY KEY(run_id, step_num),
+  FOREIGN KEY(run_id) REFERENCES runs(run_id),
+);
+
+CREATE TABLE parameters (
+  int      run_id,
+  int      step_num, 
+  varchar  param_name, 
+  varchar  param_value,
+  PRIMARY KEY(run_id, step_num, param_name)
+  FOREIGN KEY(run_id, step_num) 
+     REFERENCES operations(run_id, step_num),
+);  
+\end{verbatim}
+
+In Python, you would write three classes named \class{Run},
+\class{Operation}, and \class{Parameter}.  I won't present code for
+defining these classes, since that code is uninteresting at this
+point. Each class would contain a single method to begin with, an
+\method{__init__} method that assigns default values, such as 0 or
+\code{None}, to each attribute of the class.
+
+It's not difficult to write Python code that will create a \class{Run}
+instance and populate it with the data from the relational tables;
+with a little more effort, you can build a straightforward tool,
+usually called an object-relational mapper, to do this automatically.
+(See
+\url{http://www.amk.ca/python/unmaintained/ordb.html} for a quick hack
+at a Python object-relational mapper, and
+\url{http://www.python.org/workshops/1997-10/proceedings/shprentz.html}
+for Joel Shprentz's more successful implementation of the same idea;
+Unlike mine, Shprentz's system has been used for actual work.)
+
+However, it is difficult to make an object-relational mapper
+reasonably quick; a simple-minded implementation like mine is quite
+slow because it has to do several queries to access all of an object's
+data.  Higher performance object-relational mappers cache objects to
+improve performance, only performing SQL queries when they actually
+need to.
+
+That helps if you want to access run number 123 all of a sudden.  But
+what if you want to find all runs where a step has a parameter named
+'thickness' with a value of 2.0?  In the relational version, you have
+two unappealing choices:
+
+\begin{enumerate}
+ \item Write a specialized SQL query for this case: \code{SELECT run_id
+  FROM operations WHERE param_name = 'thickness' AND param_value = 2.0}
+  
+  If such queries are common, you can end up with lots of specialized
+  queries.  When the database tables get rearranged, all these queries
+  will need to be modified.
+
+ \item An object-relational mapper doesn't help much.  Scanning
+  through the runs means that the the mapper will perform the required
+  SQL queries to read run \#1, and then a simple Python loop can check
+  whether any of its steps have the parameter you're looking for.
+  Repeat for run \#2, 3, and so forth.  This does a vast
+  number of SQL queries, and therefore is incredibly slow.
+
+\end{enumerate}
+
+An object database such as ZODB simply stores internal pointers from
+object to object, so reading in a single object is much faster than
+doing a bunch of SQL queries and assembling the results. Scanning all
+runs, therefore, is still inefficient, but not grossly inefficient.
+
+\subsection{What is ZEO?}
+
+The ZODB comes with a few different classes that implement the
+\class{Storage} interface.  Such classes handle the job of
+writing out Python objects to a physical storage medium, which can be
+a disk file (the \class{FileStorage} class), a BerkeleyDB file
+(\class{BerkeleyStorage}), a relational database
+(\class{DCOracleStorage}), or some other medium.  ZEO adds
+\class{ClientStorage}, a new \class{Storage} that doesn't write to
+physical media but just forwards all requests across a network to a
+server.  The server, which is running an instance of the
+\class{StorageServer} class, simply acts as a front-end for some
+physical \class{Storage} class.  It's a fairly simple idea, but as
+we'll see later on in this document, it opens up many possibilities.
+
+\subsection{About this guide}
+
+The primary author of this guide works on a project which uses the
+ZODB and ZEO as its primary storage technology.  We use the ZODB to
+store process runs and operations, a catalog of available processes,
+user information, accounting information, and other data.  Part of the
+goal of writing this document is to make our experience more widely
+available.  A few times we've spent hours or even days trying to
+figure out a problem, and this guide is an attempt to gather up the
+knowledge we've gained so that others don't have to make the same
+mistakes we did while learning.
+
+This document will always be a work in progress.  If you wish to
+suggest clarifications or additional topics, please send your comments to
+\email{akuchlin@mems-exchange.org}.  
+
+\subsection{Acknowledgements}
+
+I'd like to thank the people who've pointed out inaccuracies and bugs,
+offered suggestions on the text, or proposed new topics that should be
+covered: Jeff Bauer, Willem Broekema, Thomas Guettler,
+Chris McDonough, George Runyan.

doc/guide/links.tex

+% links.tex
+% Collection of relevant links
+
+\section{Resources}
+
+ZODB HOWTO, by Michel Pelletier:
+\\
+Goes into slightly more detail about the rules for writing applications using the ZODB.
+\\
+\url{http://www.zope.org/Members/michel/HowTos/ZODB-How-To}
+
+
+Introduction to the Zope Object Database, by Jim Fulton:
+\\
+Goes into much greater detail, explaining advanced uses of the ZODB and 
+how it's actually implemented.  A definitive reference, and highly recommended.
+\\
+\url{http://www.python.org/workshops/2000-01/proceedings/papers/fulton/zodb3.html}
+
+Download link for ZEO: \\
+\url{http://www.zope.org/Products/ZEO/}
+
+

doc/guide/modules.tex

+
+% Related Modules
+%    PersistentMapping
+%    PersistentList
+%    BTree
+%    Catalog
+
+\section{Related Modules}
+
+The ZODB package includes a number of related modules that provide
+useful data types such as BTrees or full-text indexes.
+
+\subsection{\module{ZODB.PersistentMapping}}
+
+The \class{PersistentMapping} class is a wrapper for mapping objects
+that will set the dirty bit when the mapping is modified by setting or
+deleting a key.  
+
+\begin{funcdesc}{PersistentMapping}{container = \{\}}
+Create a \class{PersistentMapping} object that wraps the 
+mapping object \var{container}.  If you don't specify a
+value for \var{container}, a regular Python dictionary is used.
+\end{funcdesc}
+
+\class{PersistentMapping} objects support all the same methods as 
+Python dictionaries do.
+
+\subsection{\module{ZODB.PersistentList}}
+
+The \class{PersistentList} class is a wrapper for mutable sequence objects, 
+much as \class{PersistentMapping} is a wrapper for mappings.  
+
+\begin{funcdesc}{PersistentList}{initlist = []}
+Create a \class{PersistentList} object that wraps the 
+mutable sequence object \var{initlist}.  If you don't specify a
+value for \var{initlist}, a regular Python list is used.
+\end{funcdesc}
+
+\class{PersistentList} objects support all the same methods as 
+Python lists do.
+
+
+\subsection{B-tree Modules}
+
+%here's one: how does one implement searching? i would have expected the
+%btree objects to have ``find key nearest to this'' and ``next'' methods,
+%(like bsddb's set_location)...
+%
+%  -- erno
+
+When programming with the ZODB, Python dictionaries aren't always what
+you need.  The most important case is where you want to store a very
+large mapping.  When a Python dictionary is accessed in a ZODB, the
+whole dictionary has to be unpickled and brought into memory.  If
+you're storing something very large, such as a 100,000-entry user
+database, unpickling such a large object will be slow.  B-trees are a
+balanced tree data structure that behave like a mapping but distribute
+keys throughout a number of tree nodes.  Nodes are then only unpickled
+and brought into memory as they're accessed, so the entire tree
+doesn't have to occupy memory (unless you really are touching every
+single key).
+
+There are four different BTree modules provided.  One of them, the
+\module{BTree} module, provides the most general data type; the keys
+and values in the B-tree can be any Python object.  Some specialized B-tree
+modules require that the keys, and perhaps even the values, to be of a
+certain type, and provide faster performance because of this limitation.
+
+\begin{itemize}
+\item[ \module{IOBTree} ] requires the keys to be integers.
+The module name reminds you of this; the \module{IOBTree} module
+maps Integers to Objects.
+
+\item[ \module{OIBTree} ] requires the values to be integers,
+mapping Objects to Integers.
+
+\item[ \module{IIBTree} ] is strictest, requiring that both keys and values must be integers.
+
+\end{itemize}
+
+To use a B-tree, simply import the desired module and call the
+constructor, always named \function{BTree()}, to get a B-tree
+instance, and then use it like any other mapping:
+
+\begin{verbatim}
+import IIBTree
+iimap = IIBTree.BTree()
+iimap[1972] = 27
+\end{verbatim}
+

doc/guide/prog-zodb.tex

+
+%ZODB Programming
+%   How ZODB works (ExtensionClass, dirty bits)
+%   Installing ZODB
+%   Rules for Writing Persistent Classes
+   
+
+\section{ZODB Programming}
+
+\subsection{Installing ZODB}
+
+The ZODB forms part of Zope, but it's difficult and somewhat painful
+to extract the bits from Zope needed to support just the ZODB.
+Therefore I've assembled a distribution containing only the packages
+required to use the ZODB and ZEO, so you can install it and start
+programming right away.
+
+To download the distribution, go to my ZODB page at 
+\url{http://www.amk.ca/zodb/}.  
+The distribution is still experimental, so don't be surprised if the
+installation process runs into problems.  Please inform me of any
+difficulties you encounter.
+
+\subsubsection{Requirements}
+
+You'll need Python, of course; version 1.5.2 works with some fixes,
+and it also works with Python 2.0, which is what I primarily use.
+
+The code is packaged using Distutils, the new distribution tools for
+Python introduced in Python 2.0.  If you're using 1.5.2, first you'll
+have to get the latest Distutils release from the Distutils SIG page
+at \url{http://www.python.org/sigs/distutils-sig/download.html} and
+install it.  This is simply a matter of untarring or unzipping the
+release package, and then running \code{python setup.py install}.
+
+If you're using 1.5.2 and have installed previous versions of the
+Distutils, be sure to get the very latest version, since developing
+the ZODB distribution turned up some bugs along the way.  If you
+encounter problems compiling \file{ZODB/TimeStamp.c} or your compiler reports
+an error like ``Can't create build/temp.linux2/ExtensionClass.o: No
+such file or directory'', you need an updated version.  Old versions of
+Distutils have two bugs which affect the setup scripts.  First, for a
+long time the \code{define_macros} keyword in setup.py files didn't work due
+to a Distutils bug, so I hacked TimeStamp.c in earlier releases.  The
+Distutils have since been fixed, and the hack became unnecessary, so I
+removed it.  Second, the code that creates directories tries to be
+smart and caches them to save time by not trying to create a directory
+twice, but this code was broken in old versions.
+
+You'll need a C compiler to build the packages, because there are
+various C extension modules.  At the moment no one is making Windows
+binaries available, so you'll need a Windows development environment to use the 
+
+\subsubsection{Installing the Packages}
+
+Download the ZODB tarball containing all the packages for both ZODB
+and ZEO from \url{http://www.amk.ca/files/zodb/}.
+
+To build the packages, you must go into the individual directories and
+build and install them one by one.  They should be built and installed
+in this order:
+ 
+\begin{enumerate}
+  \item \code{zodb-basic}
+  \item ExtensionClass
+  \item ZODB
+  \item \code{BTree} and \code{BTrees}
+  \item ZEO
+\end{enumerate}
+
+In particular, you must install ExtensionClass before building the
+ZODB package; otherwise, the compilation in the ZODB package will die
+complaining that it can't find ExtensionClass.h.  You can manually
+hack the \#include path to make it work without installing
+ExtensionClass first, but that's a bit hackish.
+
+If you encounter any problems, please let me know at
+\email{akuchlin@mems-exchange.org}.
+
+\subsection{How ZODB Works}
+
+The ZODB is conceptually simple.  Python classes subclass a 
+\class{Persistent} class to become ZODB-aware. 
+Instances of persistent objects are brought in from a permanent
+storage medium, such as a disk file, when the program needs them, and
+remain cached in RAM.  The ZODB traps modifications to objects, so
+that when a statement such as \code{obj.size = 1} is executed, the
+modified object is marked as ``dirty''.  On request, any dirty objects
+are written out to permanent storage; this is called committing a
+transaction.  Transactions can also be aborted or rolled back, which
+results in any changes being discarded, dirty objects reverting to
+their initial state before the transaction began.
+
+The term ``transaction'' has a specific technical meaning in computer
+science.  It's extremely important that the contents of a database
+don't get corrupted by software or hardware crashes, and most database
+software offers protection against such corruption by supporting four
+useful properties, Atomicity, Consistency, Isolation, and Durability.
+In computer science jargon these four terms are collectively dubbed
+the ACID properties, forming an acronym from their names.  The
+definitions of the ACID properties are:
+
+\begin{itemize}
+
+\item[Atomicity] means that any changes to data made during a transaction 
+are all-or-nothing.  Either all the changes are applied, or none of
+them are.  If a program makes a bunch of modifications and then
+crashes, the database won't be partially modified, potentially leaving
+the data in an inconsistent state; instead all the changes will be
+forgotten.  That's bad, but it's better than having a
+partially-applied modification put the database into an inconsistent
+state.
+
+\item[Consistency] means that the data cannot be placed into a
+logically invalid state; sanity checks can be written and enforced.
+Usually this is done by defining a database schema, and requiring the
+data always matches the schema.  For example, this might enforce that
+the \code{order_number} attribute is always an integer, and not a
+string, tuple, or other object.
+
+\item[Isolation] means that two programs or threads running in two
+ different transactions cannot see each other's changes until they
+ commit their transactions.
+
+\item[Durability] means that once a transaction has been committed,
+a subsequent crash will not cause any data to be lost or corrupted.
+
+\end{itemize}
+
+The ZODB provides 3 of the ACID properties.  Only Consistency is not
+supported; the ZODB has no notion of a database schema, and therefore
+has no way of enforcing consistency with a schema.
+
+\subsection{Opening a ZODB}
+
+There are 3 main interfaces supplied by the ZODB:
+\class{Storage}, \class{DB}, and \class{Connection} classes. The
+\class{DB} and \class{Connection} interfaces both have single
+implementations, but there are several different classes that
+implement the \class{Storage} interface.
+
+\begin{itemize}
+ \item \class{Storage} classes are the lowest layer, and handle
+ storing and retrieving objects from some form of long-term storage.
+ A few different types of Storage have been written, such as
+ \class{FileStorage}, which uses regular disk files, and
+ \class{BerkeleyStorage}, which uses Sleepycat Software's BerkeleyDB
+ database.  You could write a new Storage that stored objects in a
+ relational database or Metakit file, for example, if that would
+ better suit your application.  Two example storages,
+ \class{DemoStorage} and \class{MappingStorage}, are available to use
+ as models if you want to write a new Storage.
+
+ \item The \class{DB} class sits on top of a storage, and mediates the
+ interaction between several connections.  One \class{DB} instance is
+ created per process.
+
+ \item Finally, the \class{Connection} class caches objects, and moves
+ them into and out of object storage.  A multi-threaded program can
+ open a separate \class{Connection} instance for each thread.
+ Different threads can then modify objects and commit their
+ modifications independently.
+
+\end{itemize}
+
+Preparing to use a ZODB requires 3 steps: you have to open the
+\class{Storage}, then create a \class{DB} instance that uses the \class{Storage}, and then get
+a \class{Connection} from the \class{DB instance}.  All this is only a few lines of
+code:
+
+\begin{verbatim}
+from ZODB import FileStorage, DB
+
+storage = FileStorage.FileStorage('/tmp/test-filestorage.fs')
+db = DB(storage)
+conn = db.open()
+\end{verbatim}
+
+Note that you can use a completely different data storage mechanism by
+changing the first line that opens a \class{Storage}; the above example uses a
+\class{FileStorage}.  In section~\ref{zeo}, ``How ZEO Works'',
+you'll see how ZEO uses this flexibility to good effect.
+
+\subsection{Writing a Persistent Class}
+
+Making a Python class persistent is quite simple; it simply needs to
+subclass from the \class{Persistent} class, as shown in this example:
+
+\begin{verbatim}
+import ZODB
+from Persistence import Persistent
+
+class User(Persistent):
+    pass
+\end{verbatim}
+
+The apparently unnecessary \code{import ZODB} statement is
+needed for the following \code{from...import} statement to work
+correctly, since the ZODB code does some magical tricks with
+importing.
+
+For simplicity, in the examples the \class{User} class will
+simply be used as a holder for a bunch of attributes.  Normally the
+class would define various methods that add functionality, but that
+has no impact on the ZODB's treatment of the class.
+
+The ZODB uses persistence by reachability; starting from a set of root
+objects, all the attributes of those objects are made persistent,
+whether they're simple Python data types or class instances.  There's
+no method to explicitly store objects in a ZODB database; simply
+assign them as an attribute of an object, or store them in a mapping,
+that's already in the database.  This chain of containment must
+eventually reach back to the root object of the database.
+
+As an example, we'll create a simple database of users that allows
+retrieving a \class{User} object given the user's ID.  First, we
+retrieve the primary root object of the ZODB using the \method{root()}
+method of the \class{Connection} instance.  The root object behaves
+like a Python dictionary, so you can just add a new key/value pair for
+your application's root object.  We'll insert a \class{BTree} object
+that will contain all the \class{User} objects.  (The
+\class{BTree} module is also included as part of Zope.)
+
+\begin{verbatim}
+dbroot = conn.root()
+
+# Ensure that a 'userdb' key is present 
+# in the root
+if not dbroot.has_key('userdb'):
+    import BTree
+    dbroot['userdb'] = BTree.BTree()
+
+userdb = dbroot['userdb']
+\end{verbatim}
+
+Inserting a new user is simple: create the \class{User} object, fill
+it with data, insert it into the \class{BTree} instance, and commit
+this transaction.
+
+\begin{verbatim}# Create new User instance
+newuser = User() 
+
+# Add whatever attributes you want to track
+newuser.id = 'amk' 
+newuser.first_name = 'Andrew' ; newuser.last_name = 'Kuchling'
+...
+
+# Add object to the BTree, keyed on the ID
+userdb[newuser.id] = newuser
+
+# Commit the change
+get_transaction().commit()
+\end{verbatim}
+
+When you import the ZODB package, it adds a new function,
+\function{get_transaction()}, to Python's collection of built-in
+functions.  \function{get_transaction()} returns a \class{Transaction}
+object, which has two important methods: \method{commit()} and
+\method{abort()}.  \method{commit()} writes any modified objects
+to disk, making the changes permanent, while \method{abort()} rolls
+back any changes that have been made, restoring the original state of
+the objects.  If you're familiar with database transactional
+semantics, this is all what you'd expect.
+
+Because the integration with Python is so complete, it's a lot like
+having transactional semantics for your program's variables, and you
+can experiment with transactions at the Python interpreter's prompt:
+
+\begin{verbatim}>>> newuser
+<User instance at 81b1f40>
+>>> newuser.first_name           # Print initial value
+'Andrew'         
+>>> newuser.first_name = 'Bob'   # Change first name
+>>> newuser.first_name           # Verify the change
+'Bob'
+>>> get_transaction().abort()    # Abort transaction
+>>> newuser.first_name           # The value has changed back
+'Andrew'
+\end{verbatim}
+
+\subsection{Rules for Writing Persistent Classes}
+
+Practically all persistent languages impose some restrictions on
+programming style, warning against constructs they can't handle or
+adding subtle semantic changes, and the ZODB is no exception.
+Happily, the ZODB's restrictions are fairly simple to understand, and
+in practice it isn't too painful to work around them.
+
+The summary of rules is as follows:
+
+\begin{itemize}
+\item If you modify a mutable object that's the value of an object's
+attribute, the ZODB can't catch that, and won't mark the object as
+dirty.  
+The solution is to either set the dirty bit yourself when you modify
+mutable objects, or use a wrapper for Python's lists and dictionaries
+(\class{PersistentList}, 
+\class{PersistentMapping})
+that will set the dirty bit properly.
+
+\item Certain of Python's special methods don't work when they're
+defined on ExtensionClasses.  The most important ones are the
+\method{__cmp__} method, and the reversed versions of binary
+arithmetic operations: \method{__radd__}, \method{__rsub__}, and so
+forth.
+
+\item Python's built-in \function{isinstance()} and \function{issubclass()}
+functions don't work properly on ExtensionClasses.  Solution: use
+custom \function{isinstance()} and \function{issubclass()} functions
+that handle ExtensionClasses correctly.
+
+\item Recent versions of the ZODB allow writing a class with 
+\method{__setattr__} , \method{__getattr__}, or \method{__delattr__} methods.  (Older versions didn't support this at all.)
+If you write such a \method{__setattr__} or \method{__delattr__} method, 
+its code has to set the dirty bit manually, 
+
+\end{itemize}
+
+Let's look at each of these rules in detail.
+
+\subsubsection{Modifying Mutable Objects}
+
+The ZODB uses various Python hooks to catch attribute accesses, and
+can trap most of the ways of modifying an object, but not all of them.
+If you modify a \class{User} object by assigning to one of its
+attributes, as in \code{userobj.first_name = 'Andrew'}, the ZODB will
+mark the object as having been changed, and it'll be written out on
+the following \method{commit()}.
+
+The most common idiom that \emph{isn't} caught by the ZODB is
+mutating a list or dictionary.  If \class{User} objects have a
+attribute named \code{friends} containing a list, calling
+\code{userobj.friends.append(otherUser)} doesn't mark
+\code{userobj} as modified; from the ZODB's point of
+view, \code{userobj.friends} was only read, and its value, which
+happened to be an ordinary Python list, was returned.  The ZODB isn't
+aware that the object returned was subsequently modified.
+
+This is one of the few quirks you'll have to remember when using the
+ZODB; if you modify a mutable attribute of an object in place, you
+have to manually mark the object as having been modified by setting
+its dirty bit to true.  This is done by setting the
+\member{_p_changed} attribute of the object to true:
+
+\begin{verbatim}
+userobj.friends.append(otherUser)
+userobj._p_changed = 1
+\end{verbatim}
+
+An obsolete way of doing this that's still supported is calling the
+\method{__changed__()} method instead, but setting \member{_p_changed} 
+is the preferred way.
+
+You can hide the implementation detail of having to mark objects as
+dirty by designing your class's API to not use direct attribute
+access; instead, you can use the Java-style approach of accessor
+methods for everything, and then set the dirty bit within the accessor
+method.  For example, you might forbid accessing the \code{friends}
+attribute directly, and add a \method{get_friend_list()} accessor and
+an \method{add_friend()} modifier method to the class.  \method{add_friend()}
+would then look like this:
+
+\begin{verbatim}
+    def add_friend(self, friend):
+        self.friends.append(otherUser)
+        self._p_changed = 1
+\end{verbatim}
+
+Alternatively, you could use a ZODB-aware list or mapping type that
+handles the dirty bit for you.  The ZODB comes with a
+\class{PersistentMapping} class, and I've contributed a
+\class{PersistentList} class that's included in my ZODB distribution, 
+and may make it into a future upstream release of Zope.
+
+% XXX It'd be nice to discuss what happens when an object is ``ghosted'' (e.g.
+% you set an object's _p_changed = None).  The __p_deactivate__ method should
+% not be used (it's also obsolete). 
+
+\subsubsection{Some Special Methods Don't Work}
+
+Don't bother defining certain special methods on
+ExtensionClasses, because they won't work.  Most notably, the
+\method{__cmp__} method on an ExtensionClass will never be called.
+Neither will the reversed versions of binary arithmetic operations,
+such as \method{__radd__} and \method{__rsub__}.
+
+This is a moderately annoying limitation.  It means that the
+\class{PersistentList} class can't implement comparisons with regular
+sequence objects, and therefore statements such as 
+\verb|if perslist==[]| don't do what you expect; instead of performing the correct
+comparison, they return some arbitrary fixed result, so the \code{if}
+statement will always be true or always be false.  There is no good
+solution to this problem at the moment, so all you can do is design
+class interfaces that don't need to overload
+\method{__cmp__} or the \method{__r*__} methods.
+
+This limitation is mostly Python's fault.  As of Python 2.1, the most
+recent version at this writing, the code which handles comparing two
+Python objects contains a hard-wired check for objects that are class
+instances, which means that \code{type(obj) == types.InstanceType}.
+The code inside the Python interpreter looks like this:
+
+\begin{verbatim}
+/* Code to compare objects v and w */
+if (PyInstance_Check(v) || PyInstance_Check(w))
+        return PyInstance_DoBinOp(v, w, "__cmp__", "__rcmp__", do_cmp);
+/* Do usual Python comparison of v,w */
+c = PyObject_Compare(v, w);
+\end{verbatim}
+
+While ExtensionClasses try to behave as much like regular Python
+instances as possible, they are still not instances, and
+\function{type()} doesn't return the \code{InstanceType} object, so 
+no attempt is ever made to call \method{__cmp__}.  Perhaps Python 2.2
+will repair this.
+
+\subsubsection{Fixing \function{isinstance} and \function{issubclass}}
+
+Python's built-in functions 
+\function{isinstance()} and \function{issubclass} don't
+work on ExtensionClass instances, for much the same reason that 
+\method{__cmp__} is never called; in some bits of the Python core code,
+branches are taken only if an object is of the \class{InstanceType}
+type, and this can never be true for an ExtensionClass instance.
+Python 2.1 tried to fix this, and changed these functions slightly in
+an effort to make them work for ExtensionClasses; unfortunately, the
+changes didn't work.
+
+The solution is to use customized versions of these functions that
+handle ExtensionClasses specially and fall back to the built-in
+version otherwise.  Here are the versions we've written at the MEMS Exchange:
+
+\begin{verbatim}
+# The built-in 'isinstance()' and 'issubclass()' won't work on
+# ExtensionClasses, so you have to use the versions supplied here.
+# (But those versions work fine on regular instances and classes too,
+# so you should *always* use them.)
+
+def issubclass (class1, class2):
+    """A version of 'issubclass' that works with extension classes
+    as well as regular Python classes.
+    """
+
+    # Both class objects are regular Python classes, so use the
+    # built-in 'issubclass()'.
+    if type(class1) is ClassType and type(class2) is ClassType:
+        return __builtin__.issubclass(class1, class2)
+
+    # Both so-called class objects have a '__bases__' attribute: ie.,
+    # they aren't regular Python classes, but they sure look like them.
+    # Assume they are extension classes and reimplement what the builtin
+    # 'issubclass()' does behind the scenes.
+    elif hasattr(class1, '__bases__') and hasattr(class2, '__bases__'):
+        # XXX it appears that "ec.__class__ is type(ec)" for an
+        # extension class 'ec': could we/should we use this as an
+        # additional check for extension classes?
+
+        # Breadth-first traversal of class1's superclass tree.  Order
+        # doesn't matter because we're just looking for a "yes/no"
+        # answer from the tree; if we were trying to resolve a name,
+        # order would be important!
+        stack = [class1]
+        while stack:
+            if stack[0] is class2:
+                return 1
+            stack.extend(list(stack[0].__bases__))
+            del stack[0]
+        else:
+            return 0
+
+    # Not a regular class, not an extension class: blow up for consistency
+    # with builtin 'issubclass()"
+    else:
+        raise TypeError, "arguments must be class or ExtensionClass objects"
+
+# issubclass ()
+
+def isinstance (object, klass):
+    """A version of 'isinstance' that works with extension classes
+    as well as regular Python classes."""
+
+    if type(klass) is TypeType:
+        return __builtin__.isinstance(object, klass)
+    elif hasattr(object, '__class__'):
+        return issubclass(object.__class__, klass)
+    else:
+        return 0
+\end{verbatim}
+
+I'd recommend putting these functions in a module that always gets
+imported.  The convention on my work project is to put them in
+\file{mems/lib/base.py}, which contains various fundamental classes
+and functions for our system, and access them like this:
+
+\begin{verbatim}
+from mems.lib import base
+...
+if base.isinstance(object, Class): ...
+\end{verbatim}
+
+Don't insert the modified functions into Python's
+\module{__builtin__} module, or import just the
+\function{isinstance()} and \function{issubclass} functions.  
+If you consistently use \function{base.isinstance()}, then forgetting
+to import the \module{base} module will result in a
+\exception{NameError} exception.  In the
+case of a forgotten import, calling the functions directly would use
+Python's built-in versions, leading to subtle bugs that might not be
+noticed for some time.
+
+\subsubsection{\method{__getattr__}, \method{__delattr__}, and \method{__setattr__}}
+
+Recent versions of ZODB allow writing persistent classes that have
+\method{__getattr__}, \method{__delattr__}, or \method{__setattr__}
+methods.  The one minor complication is that the machinery for
+automatically detecting changes to the object is disabled while the
+\method{__getattr__}, \method{__delattr__}, or \method{__setattr__}
+method is executing.  This means that if the object is modified, the
+object should be marked as dirty by setting the object's
+\member{_p_changed} method to true.
+
+\subsection{Writing Persistent Classes}
+
+Now that we've looked at the basics of programming using the ZODB,
+we'll turn to some more subtle tasks that are likely to come up for
+anyone using the ZODB in a production system.
+
+\subsubsection{Changing Instance Attributes}
+
+Ideally, before making a class persistent you would get its interface
+right the first time, so that no attributes would ever need to be
+added, removed, or have their interpretation change over time.  It's a
+worthy goal, but also an impractical one unless you're gifted with
+perfect knowledge of the future.  Such unnatural foresight can't be
+required of any person, so you therefore have to be prepared to handle
+such structural changes gracefully.  In object-oriented database
+terminology, this is a schema update.  The ZODB doesn't have an actual
+schema specification, but you're changing the software's expectations
+of the data contained by an object, so you're implicitly changing the
+schema.
+
+One way to handle such a change is to write a one-time conversion
+program that will loop over every single object in the database and
+update them to match the new schema.  This can be easy if your network
+of object references is quite structured, making it easy to find all
+the instances of the class being modified.  For example, if all
+\class{User} objects can be found inside a single dictionary or
+B-tree, then it would be a simple matter to loop over every
+\class{User} instance with a \keyword{for} statement.
+This is more difficult if your object graph is less structured; if
+\class{User} objects can be found as attributes of any number of
+different class instances, then there's no longer any easy way to find
+them all, short of writing a generalized object traversal function
+that would walk over every single object in a ZODB, checking each one
+to see if it's an instance of \class{User}.  
+\footnote{XXX is there a convenience method for walking the object graph hiding
+somewhere inside DC's code?  Should there be a utility method for
+doing this?  Should I write one and include it in this section?}
+Some OODBs support a feature called extents, which allow quickly
+finding all the instances of a given class, no matter where they are
+in the object graph; unfortunately the ZODB doesn't offer extents as a
+feature.
+
+XXX Rest of section not written yet: __getstate__/__setstate__
+

doc/guide/storages.tex

+
+% Storages
+%    FileStorage
+%    BerkeleyStorage
+%    OracleStorage
+
+\section{Storages}
+
+This chapter will examine the different \class{Storage} subclasses
+that are considered stable, discuss their varying characteristics, and
+explain how to administer them.
+
+\subsection{Using Multiple Storages}
+
+XXX explain mounting substorages
+
+\subsection{FileStorage}
+
+\subsection{BerkeleyStorage}
+
+\subsection{OracleStorage}
+

doc/guide/transactions.tex

+%Transactions and Versioning
+%   Committing and Aborting
+%   Subtransactions
+%   Undoing
+%   Versions
+%   Multithreaded ZODB Programs
+   
+
+\section{Transactions and Versioning}
+
+%\subsection{Committing and Aborting}
+% XXX There seems very little to say about commit/abort...
+
+\subsection{Subtransactions}
+
+Subtransactions can be created within a transaction.  Each
+subtransaction can be individually committed and aborted, but the
+changes within a subtransaction are not truly committed until the
+containing transaction is committed.
+
+The primary purpose of subtransactions is to decrease the memory usage
+of transactions that touch a very large number of objects.  Consider a
+transaction during which 200,000 objects are modified.  All the
+objects that are modified in a single transaction have to remain in
+memory until the transaction is committed, because the ZODB can't
+discard them from the object cache.  This can potentially make the
+memory usage quite large.  With subtransactions, a commit can be be
+performed at intervals, say, every 10,000 objects.  Those 10,000
+objects are then written to permanent storage and can be purged from
+the cache to free more space.
+
+To commit a subtransaction instead of a full transaction, 
+pass a true value to the \method{commit()}
+or \method{abort()} method of the \class{Transaction} object.
+
+\begin{verbatim}
+# Commit a subtransaction
+get_transaction().commit(1)	
+
+# Abort a subtransaction
+get_transaction().abort(1)   
+\end{verbatim}
+
+A new subtransaction is automatically started on committing or
+aborting the previous subtransaction.
+
+
+\subsection{Undoing Changes}
+
+Some types of \class{Storage} support undoing a transaction even after
+it's been committed.  You can tell if this is the case by calling the
+\method{supportsUndo()} method of the \class{DB} instance, which
+returns true if the underlying storage supports undo.  Alternatively
+you can call the \method{supportsUndo()} method on the underlying
+storage instance.
+
+If a database supports undo, then the \method{undoLog(\var{start},
+\var{end}\optional{, func})} method on the \class{DB} instance returns
+the log of past transactions, returning transactions between the times
+\var{start} and \var{end}, measured in seconds from the epoch.   
+If present, \var{func} is a function that acts as a filter on the
+transactions to be returned; it's passed a dictionary representing
+each transaction, and only transactions for which \var{func} returns
+true will be included in the list of transactions returned to the
+caller of \method{undoLog()}.  The dictionary contains keys for
+various properties of the transaction.  The most important keys are
+\samp{id}, for the transaction ID, and \samp{time}, for the time at
+which the transaction was committed.  
+
+\begin{verbatim}
+>>> print storage.undoLog(0, sys.maxint)
+[{'description': '',
+  'id': 'AzpGEGqU/0QAAAAAAAAGMA',
+  'time': 981126744.98,
+  'user_name': ''},
+ {'description': '',
+  'id': 'AzpGC/hUOKoAAAAAAAAFDQ',
+  'time': 981126478.202,
+  'user_name': ''}
+  ...
+\end{verbatim}
+
+To store a description and a user name on a commit, get the current
+transaction and call the \method{note(\var{text})} method to store a
+description, and the
+\method{setUser(\var{user_name})} method to store the user name.  
+While \method{setUser()} overwrites the current user name and replaces
+it with the new value, the \method{note()} method always adds the text
+to the transaction's description, so it can be called several times to
+log several different changes made in the course of a single
+transaction.
+
+\begin{verbatim}
+get_transaction().setUser('amk')
+get_transaction().note('Change ownership')
+\end{verbatim}
+
+To undo a transaction, call the \method{DB.undo(\var{id})} method,
+passing it the ID of the transaction to undo.  If the transaction
+can't be undone, a \exception{ZODB.POSException.UndoError} exception
+will be raised, with the message ``non-undoable
+transaction''.  Usually this will happen because later transactions
+modified the objects affected by the transaction you're trying to
+undo.
+
+\subsection{Versions}
+
+While many subtransactions can be contained within a single regular
+transaction, it's also possible to contain many regular transactions
+within a long-running transaction, called a version in ZODB
+terminology.  Inside a version, any number of transactions can be
+created and committed or rolled back, but the changes within a version
+are not made visible to other connections to the same ZODB.
+
+Not all storages support versions, but you can test for versioning
+ability by calling \method{supportsVersions()} method of the
+\class{DB} instance, which returns true if the underlying storage
+supports versioning.
+
+A version can be selected when creating the \class{Connection}
+instance using the \method{DB.open(\optional{\var{version}})} method.
+The \var{version} argument must be a string that will be used as the
+name of the version.
+
+\begin{verbatim}
+vers_conn = db.open(version='Working version')
+\end{verbatim}
+
+Transactions can then be committed and aborted using this versioned
+connection.  Other connections that don't specify a version, or
+provide a different version name, will not see changes committed
+within the version named \samp{Working~version}.  To commit or abort a
+version, which will either make the changes visible to all clients or
+roll them back, call the \method{DB.commitVersion()} or
+\method{DB.abortVersion()} methods.
+XXX what are the source and dest arguments for?
+
+The ZODB makes no attempt to reconcile changes between different
+versions.  Instead, the first version which modifies an object will
+gain a lock on that object.  Attempting to modify the object from a
+different version or from an unversioned connection will cause a
+\exception{ZODB.POSException.VersionLockError} to be raised:
+
+\begin{verbatim}
+from ZODB.POSException import VersionLockError
+
+try:
+    get_transaction().commit()
+except VersionLockError, (obj_id, version):
+    print ('Cannot commit; object %s '
+           'locked by version %s' % (obj_id, version))
+\end{verbatim}
+
+The exception provides the ID of the locked object, and the name of
+the version having a lock on it.
+
+\subsection{Multithreaded ZODB Programs}
+
+ZODB databases can be accessed from multithreaded Python programs.
+The \class{Storage} and \class{DB} instances can be shared among
+several threads, as long as individual \class{Connection} instances
+are created for each thread.  
+
+XXX I can't think of anything else to say about multithreaded ZODB
+programs.  Suggestions?  An example program?
+

doc/guide/zeo.tex

+
+% ZEO
+%    Installing ZEO
+%    How ZEO works (ClientStorage)
+%    Configuring ZEO
+   
+\section{ZEO}
+\label{zeo}
+
+\subsection{How ZEO Works}
+
+The ZODB, as I've described it so far, can only be used within a
+single Python process (though perhaps with multiple threads).  ZEO,
+Zope Enterprise Objects, extends the ZODB machinery to provide access
+to objects over a network.  The name "Zope Enterprise Objects" is a
+bit misleading; ZEO can be used to store Python objects and access
+them in a distributed fashion without Zope ever entering the picture.
+The combination of ZEO and ZODB is essentially a Python-specific
+object database.
+
+ZEO consists of about 1400 lines of Python code.  The code is
+relatively small because it contains only code for a TCP/IP server,
+and for a new type of Storage, \class{ClientStorage}.
+\class{ClientStorage} doesn't use disk files at all; it simply
+makes remote procedure calls to the server, which then passes them on
+a regular \class{Storage} class such as \class{FileStorage}.  The
+following diagram lays out the system:
+
+XXX insert diagram here later
+
+Any number of processes can create a \class{ClientStorage}
+instance, and any number of threads in each process can be using that
+instance.  \class{ClientStorage} aggressively caches objects
+locally, so in order to avoid using stale data, the ZEO server sends
+an invalidate message to all the connected \class{ClientStorage}
+instances on every write operation.  The invalidate message contains
+the object ID for each object that's been modified, letting the
+\class{ClientStorage} instances delete the old data for the
+given object from their caches.
+
+This design decision has some consequences you should be aware of.
+First, while ZEO isn't tied to Zope, it was first written for use with
+Zope, which stores HTML, images, and program code in the database.  As
+a result, reads from the database are \emph{far} more frequent than
+writes, and ZEO is therefore better suited for read-intensive
+applications.  If every \class{ClientStorage} is writing to the
+database all the time, this will result in a storm of invalidate
+messages being sent, and this might take up more processing time than
+the actual database operations themselves.
+
+On the other hand, for applications that have few writes in comparison
+to the number of read accesses, this aggressive caching can be a major
+win.  Consider a Slashdot-like discussion forum that divides the load
+among several Web servers.  If news items and postings are represented
+by objects and accessed through ZEO, then the most heavily accessed
+objects -- the most recent or most popular postings -- will very
+quickly wind up in the caches of the
+\class{ClientStorage} instances on the front-end servers.  The
+back-end ZEO server will do relatively little work, only being called
+upon to return the occasional older posting that's requested, and to
+send the occasional invalidate message when a new posting is added.
+The ZEO server isn't going to be contacted for every single request,
+so its workload will remain manageable.
+
+\subsection{Installing ZEO}
+
+This section covers how to install the ZEO package, and how to 
+configure and run a ZEO Storage Server on a machine. 
+
+\subsubsection{Requirements}
+
+To run a ZEO server, you'll need Python 1.5.2 or 2.0, and the ZODB
+packages from \url{http://www.amk.ca/files/zodb/}
+have to be installed.  
+
+\emph{Note for Python 1.5.2 users}: ZEO requires updated versions
+of the \module{asyncore.py} and \module{asynchat.py} modules that are
+included in 1.5.2's standard library.  Current versions of the ZODB
+distribution install private versions of these modules, so you
+shouldn't need to grab updated versions yourself.  (The symptom of
+this problem is a traceback on attempting to run a ZEO client program:
+the traceback is ``TypeError: too many arguments; expected 2, got 3''
+around line 100 of \file{smac.py}.
+
+\subsubsection{Installation}
+
+Installing the ZEO package is easy.  Just run \code{python setup.py
+install}.  This will install the ZEO/ package into your Python
+installation, and copy various files into their proper locations:
+\file{zeo.conf} will be put into \file{/usr/local/etc/}, a \file{zeo} startup
+script will be put in \file{/etc/rc.d/init.d/}, and the \file{zeod}
+daemon program will be placed in \file{/usr/local/bin}.
+
+\subsection{Configuring and Running a ZEO Server}
+
+Edit \code{/usr/local/etc/zeo.conf} appropriately for your desired
+setup.  This configuration file controls the port on which ZEO will
+listen for connections, the user and group IDs under which the server
+will be executed, and the location of the concrete \class{Storage}
+object that will be made network-accessible.
+ 
+\subsection{Testing the ZEO Installation}
+
+Once a ZEO server is up and running, using it is just like using ZODB
+with a more conventional disk-based storage; no new programming
+details are introduced by using a remote server.  The only difference
+is that programs must create a \class{ClientStorage} instance instead
+of a \class{FileStorage} instance.  From that point onward, ZODB-based
+code is happily unaware that objects are being retrieved from a ZEO
+server, and not from the local disk.
+
+As an example, and to test whether ZEO is working correctly, try
+running the following lines of code, which will connect to the server,
+add some bits of data to the root of the ZODB, and commits the
+transaction:
+
+\begin{verbatim}
+from ZEO import ClientStorage
+from ZODB import DB
+
+# Change next line to connect to your ZEO server
+addr = ('kronos.example.com', 1975)
+storage = ClientStorage.ClientStorage(addr)
+db = DB(storage)
+conn = db.open()
+root = conn.root()
+
+# Store some things in the root
+root['list'] = ['a', 'b', 1.0, 3]
+root['dict'] = {'a':1, 'b':4}
+
+# Commit the transaction
+get_transaction().commit()
+\end{verbatim}
+
+If this code runs properly, then your ZEO server is working correctly.
+
+\subsection{ZEO Programming Notes}
+
+XXX The Connection.sync() method and its necessity (if it works at all!) 
+
+% That doesn't work.  I tested it.  sync() doesn't seem to get into
+% the asyncore loop.  One of us should probably look into adding an
+% API for this when we have some free time.  It would be a nice
+% small project that would get into ZODB's guts.
+
+
+
+
+\subsection{Sample Application: chatter.py}
+
+For an example application, we'll build a little chat application.
+What's interesting is that none of the application's code deals with
+network programming at all; instead, an object will hold chat
+messages, and be magically shared between all the clients through ZEO.
+I won't present the complete script here; it's included in my ZODB
+distribution, and you can download it from
+\url{http://www.amk.ca/zodb/demos/}.  Only the interesting portions of
+the code will be covered here.
+
+The basic data structure is the \class{ChatSession} object,
+which provides an \method{add_message()} method that adds a
+message, and a \method{new_messages()} method that returns a list
+of new messages that have accumulated since the last call to
+\method{new_messages()}.  Internally, \class{ChatSession}
+maintains a B-tree that uses the time as the key, and stores the
+message as the corresponding value.
+
+The constructor for \class{ChatSession} is pretty simple; it simply
+creates an attribute containing a B-tree:
+
+\begin{verbatim}
+class ChatSession(Persistent):
+    def __init__(self, name):
+        self.name = name
+        # Internal attribute: _messages holds all the chat messages.        
+        self._messages = BTree.BTree()        
+\end{verbatim}
+
+\method{add_message()} has to add a message to the
+\code{_messages} B-tree.  A complication is that it's possible
+that some other client is trying to add a message at the same time;
+when this happens, the client that commits first wins, and the second
+client will get a \exception{ConflictError} exception when it tries to
+commit.  For this application, \exception{ConflictError} isn't serious
+but simply means that the operation has to be retried; other
+applications might treat it as a fatal error.  The code uses
+\code{try...except...else} inside a \code{while} loop,
+breaking out of the loop when the commit works without raising an
+exception.
+
+\begin{verbatim}
+    def add_message(self, message):
+        """Add a message to the channel.
+        message -- text of the message to be added
+        """
+
+        while 1:
+            try:
+                now = time.time()
+                self._messages[now] = message
+                get_transaction().commit()
+            except ConflictError:
+                # Conflict occurred; this process should pause and
+                # wait for a little bit, then try again.
+                time.sleep(.2)
+                pass
+            else:
+                # No ConflictError exception raised, so break
+                # out of the enclosing while loop.
+                break
+        # end while
+\end{verbatim}
+
+\method{new_messages()} introduces the use of \textit{volatile}
+attributes.  Attributes of a persistent object that begin with
+\code{_v_} are considered volatile and are never stored in the
+database.  \method{new_messages()} needs to store the last time
+the method was called, but if the time was stored as a regular
+attribute, its value would be committed to the database and shared
+with all the other clients.  \method{new_messages()} would then
+return the new messages accumulated since any other client called
+\method{new_messages()}, which isn't what we want.
+
+\begin{verbatim}
+    def new_messages(self):
+        "Return new messages."
+
+        # self._v_last_time is the time of the most recent message
+        # returned to the user of this class. 
+        if not hasattr(self, '_v_last_time'):
+            self._v_last_time = 0
+
+        new = []
+        T = self._v_last_time
+
+        for T2, message in self._messages.items():
+            if T2 > T:
+                new.append(message)
+                self._v_last_time = T2
+
+        return new
+\end{verbatim}
+
+This application is interesting because it uses ZEO to easily share a
+data structure; ZEO and ZODB are being used for their networking
+ability, not primarily for their data storage ability.  I can foresee
+many interesting applications using ZEO in this way:
+
+\begin{itemize}
+  \item With a Tkinter front-end, and a cleverer, more scalable data
+  structure, you could build a shared whiteboard using the same
+  technique.
+
+  \item A shared chessboard object would make writing a networked chess
+  game easy.  
+
+  \item You could create a Python class containing a CD's title and
+  track information.  To make a CD database, a read-only ZEO server
+  could be opened to the world, or an HTTP or XML-RPC interface could
+  be written on top of the ZODB.
+
+  \item A program like Quicken could use a ZODB on the local disk to
+  store its data.  This avoids the need to write and maintain
+  specialized I/O code that reads in your objects and writes them out;
+  instead you can concentrate on the problem domain, writing objects
+  that represent cheques, stock portfolios, or whatever.
+
+\end{itemize}
+

doc/guide/zodb.tex

+\documentclass{howto}
+
+\title{ZODB/ZEO Programming Guide}
+\release{0.03}
+\date{\today}
+
+\author{A.M.\ Kuchling}
+\authoraddress{akuchlin@mems-exchange.org}
+
+\begin{document}
+\maketitle
+\tableofcontents
+
+\copyright{Copyright 2002 A.M. Kuchling.
+      Permission is granted to copy, distribute and/or modify this document
+      under the terms of the GNU Free Documentation License, Version 1.1
+      or any later version published by the Free Software Foundation;
+      with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
+      A copy of the license is included in the appendix entitled ``GNU
+      Free Documentation License''.}
+
+\input{introduction}
+\input{prog-zodb}
+\input{zeo}
+\input{transactions}
+%\input{storages}
+%\input{indexing}
+%\input{admin}
+\input{modules}
+
+\appendix
+\input links.tex
+\input gfdl.tex
+
+\end{document}

doc/guide/zodb/about.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>About this document ...</title>
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+<tr>
+<td><A HREF="node53.html"><img src="/python/writing/icons/previous.gif"
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+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node53.html">ADDENDUM: How to use</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="zodb.html">ZODB/ZEO Programming Guide</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H1><A NAME="SECTION000900000000000000000">
+About this document ...</A>
+</H1>
+ <strong>ZODB/ZEO Programming Guide</strong>,
+February 8, 2002, Release 0.03
+<p> This document was generated using the <a
+    href="http://saftsack.fs.uni-bayreuth.de/~latex2ht/">
+    <strong>LaTeX</strong>2<tt>HTML</tt></a> translator.
+</p>
+
+<p> <a
+    href="http://saftsack.fs.uni-bayreuth.de/~latex2ht/">
+    <strong>LaTeX</strong>2<tt>HTML</tt></a> is Copyright &copy;
+  1993, 1994, 1995, 1996, 1997, <a
+    href="http://cbl.leeds.ac.uk/nikos/personal.html">Nikos
+    Drakos</a>, Computer Based Learning Unit, University of
+  Leeds, and Copyright &copy; 1997, 1998, <a
+    href="http://www.maths.mq.edu.au/~ross/">Ross
+    Moore</a>, Mathematics Department, Macquarie University,
+  Sydney.
+</p>
+
+<p> The application of <a
+    href="http://saftsack.fs.uni-bayreuth.de/~latex2ht/">
+    <strong>LaTeX</strong>2<tt>HTML</tt></a> to the Python
+  documentation has been heavily tailored by Fred L. Drake,
+  Jr.  Original navigation icons were contributed by Christopher
+  Petrilli.
+</p>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node53.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
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+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
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+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
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+<b class="navlabel">Up:</b> <a class="sectref" HREF="zodb.html">ZODB/ZEO Programming Guide</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/contents.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>Contents</title>
+<META NAME="description" CONTENT="Contents">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node2.html">
+<LINK REL="previous" HREF="zodb.html">
+<LINK REL="up" HREF="zodb.html">
+<LINK REL="next" HREF="node2.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="zodb.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="zodb.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node2.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="zodb.html">ZODB/ZEO Programming Guide</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="zodb.html">ZODB/ZEO Programming Guide</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node2.html">1 Introduction</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+<BR>
+<BR><H2><A NAME="SECTION000100000000000000000">
+Contents</A>
+</H2>
+<!--Table of Contents-->
+
+<UL>
+<LI><A href="contents.html">Contents</a>
+<LI><A href="node2.html">1 Introduction</a>
+<UL>
+<LI><A href="node3.html">1.1 What is the ZODB?</a>
+<LI><A href="node4.html">1.2 OODBs vs. Relational DBs</a>
+<LI><A href="node5.html">1.3 What is ZEO?</a>
+<LI><A href="node6.html">1.4 About this guide</a>
+<LI><A href="node7.html">1.5 Acknowledgements</a>
+</ul>
+<LI><A href="node8.html">2 ZODB Programming</a>
+<UL>
+<LI><A href="node9.html">2.1 Installing ZODB</a>
+<LI><A href="node12.html">2.2 How ZODB Works</a>
+<LI><A href="node13.html">2.3 Opening a ZODB</a>
+<LI><A href="node14.html">2.4 Writing a Persistent Class</a>
+<LI><A href="node15.html">2.5 Rules for Writing Persistent Classes</a>
+<LI><A href="node20.html">2.6 Writing Persistent Classes</a>
+</ul>
+<LI><A href="zeo.html">3 ZEO</a>
+<UL>
+<LI><A href="node23.html">3.1 How ZEO Works</a>
+<LI><A href="node24.html">3.2 Installing ZEO</a>
+<LI><A href="node27.html">3.3 Configuring and Running a ZEO Server</a>
+<LI><A href="node28.html">3.4 Testing the ZEO Installation</a>
+<LI><A href="node29.html">3.5 ZEO Programming Notes</a>
+<LI><A href="node30.html">3.6 Sample Application: chatter.py</a>
+</ul>
+<LI><A href="node31.html">4 Transactions and Versioning</a>
+<UL>
+<LI><A href="node32.html">4.1 Subtransactions</a>
+<LI><A href="node33.html">4.2 Undoing Changes</a>
+<LI><A href="node34.html">4.3 Versions</a>
+<LI><A href="node35.html">4.4 Multithreaded ZODB Programs</a>
+</ul>
+<LI><A href="node36.html">5 Related Modules</a>
+<UL>
+<LI><A href="node37.html">5.1 <tt class="module">ZODB.PersistentMapping</tt></a>
+<LI><A href="node38.html">5.2 <tt class="module">ZODB.PersistentList</tt></a>
+<LI><A href="node39.html">5.3 B-tree Modules</a>
+</ul>
+<LI><A href="node40.html">A. Resources</a>
+<LI><A href="node41.html">B. GNU Free Documentation License</a>
+<UL>
+<LI><A href="node42.html">Preamble</a>
+<LI><A href="node43.html">B..1 Applicability and Definitions</a>
+<LI><A href="node44.html">B..2 Verbatim Copying</a>
+<LI><A href="node45.html">B..3 Copying in Quantity</a>
+<LI><A href="node46.html">B..4 Modifications</a>
+<LI><A href="node47.html">B..5 Combining Documents</a>
+<LI><A href="node48.html">B..6 Collections of Documents</a>
+<LI><A href="node49.html">B..7 Aggregation With Independent Works</a>
+<LI><A href="node50.html">B..8 Translation</a>
+<LI><A href="node51.html">B..9 Termination</a>
+<LI><A href="node52.html">B..10 Future Revisions of This Licence</a>
+<LI><A href="node53.html">ADDENDUM: How to use this License for your documents</a>
+</ul>
+<LI><A href="about.html">About this document ...</a>
+</ul>
+<!--End of Table of Contents-->
+<P>
+&#169;Copyright 2002 A.M. Kuchling.
+      Permission is granted to copy, distribute and/or modify this document
+      under the terms of the GNU Free Documentation License, Version 1.1
+      or any later version published by the Free Software Foundation;
+      with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
+      A copy of the license is included in the appendix entitled ``GNU
+      Free Documentation License''.
+
+<P>
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="zodb.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="zodb.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node2.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="zodb.html">ZODB/ZEO Programming Guide</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="zodb.html">ZODB/ZEO Programming Guide</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node2.html">1 Introduction</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/images.tex

+\batchmode
+\documentclass{howto}
+\RequirePackage{ifthen}
+
+
+
+\title{ZODB/ZEO Programming Guide}
+\release{0.03}
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+
+
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+\newcommand\lthtmlindisplaymathZ{\egroup %
+  \centerinlinemath\lthtmllogmath\lthtmlsetmath}
+\def\lthtmlsetinline{\hbox{\vrule width.1em \vtop{\vbox{%
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+  \ifdim\hsize>\wd\sizebox \hrule depth1pt\fi}}}
+\def\lthtmlsetmath{\hbox{\vrule width.1em\kern-.05em\vtop{\vbox{%
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+  \ifdim\dp\sizebox>0pt\kern.1em\fi \kern0.8 pt%
+  \ifdim\hsize>\wd\sizebox \hrule depth1pt\fi}}}
+\def\centerinlinemath{%
+  \dimen1=\ifdim\ht\sizebox<\dp\sizebox \dp\sizebox\else\ht\sizebox\fi
+  \advance\dimen1by.5pt \vrule width0pt height\dimen1 depth\dimen1 
+ \dp\sizebox=\dimen1\ht\sizebox=\dimen1\relax}
+
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+  \ifdim\wd\sizebox<\hsize\expandafter\hfill\fi \expandafter\vfill
+  \else\expandafter\vss\fi}%
+\providecommand{\selectlanguage}[1]{}%
+\makeatletter \tracingstats = 1 
+
+
+\begin{document}
+\pagestyle{empty}\thispagestyle{empty}\lthtmltypeout{}%
+\lthtmltypeout{latex2htmlLength hsize=\the\hsize}\lthtmltypeout{}%
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+\stepcounter{subsection}
+\stepcounter{subsection}
+\stepcounter{subsection}
+\stepcounter{section}
+\stepcounter{subsection}
+\stepcounter{subsection}
+\stepcounter{subsection}
+\appendix
+\stepcounter{section}
+\stepcounter{section}
+{\newpage\clearpage
+\lthtmlinlinemathA{tex2html_wrap_inline847}%
+$\copyright$%
+\lthtmlinlinemathZ
+\lthtmlcheckvsize\clearpage}
+
+\stepcounter{subsection}
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+\stepcounter{subsection}
+\stepcounter{subsection}
+
+\end{document}

doc/guide/zodb/index.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>ZODB/ZEO Programming Guide</title>
+<META NAME="description" CONTENT="ZODB/ZEO Programming Guide">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" href="contents.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><A href="contents.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Next:</b> <a class="sectref" href="contents.html">Contents</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<div class="titlepage">
+<center>
+<h1>ZODB/ZEO Programming Guide</h1>
+<p><b><font size="+2">A.M. Kuchling</font></b></p>
+<p>akuchlin@mems-exchange.org</p>
+<p><strong>Release 0.03</strong><br>
+<strong>February 8, 2002</strong></p>
+<p>
+</center>
+</div>
+
+<p><hr>
+<!--Table of Child-Links-->
+<A NAME="CHILD_LINKS"></a>
+
+<UL>
+<LI><A href="contents.html">Contents</a>
+<LI><A href="node2.html">1 Introduction</a>
+<UL>
+<LI><A href="node3.html">1.1 What is the ZODB?</a>
+<LI><A href="node4.html">1.2 OODBs vs. Relational DBs</a>
+<LI><A href="node5.html">1.3 What is ZEO?</a>
+<LI><A href="node6.html">1.4 About this guide</a>
+<LI><A href="node7.html">1.5 Acknowledgements</a>
+</ul>
+<LI><A href="node8.html">2 ZODB Programming</a>
+<UL>
+<LI><A href="node9.html">2.1 Installing ZODB</a>
+<UL>
+<LI><A href="node10.html">2.1.1 Requirements</a>
+<LI><A href="node11.html">2.1.2 Installing the Packages</a>
+</ul>
+<LI><A href="node12.html">2.2 How ZODB Works</a>
+<LI><A href="node13.html">2.3 Opening a ZODB</a>
+<LI><A href="node14.html">2.4 Writing a Persistent Class</a>
+<LI><A href="node15.html">2.5 Rules for Writing Persistent Classes</a>
+<UL>
+<LI><A href="node16.html">2.5.1 Modifying Mutable Objects</a>
+<LI><A href="node17.html">2.5.2 Some Special Methods Don't Work</a>
+<LI><A href="node18.html">2.5.3 Fixing <tt class="function">isinstance</tt> and <tt class="function">issubclass</tt></a>
+<LI><A href="node19.html">2.5.4 <tt class="method">__getattr__</tt>, <tt class="method">__delattr__</tt>, and <tt class="method">__setattr__</tt></a>
+</ul>
+<LI><A href="node20.html">2.6 Writing Persistent Classes</a>
+<UL>
+<LI><A href="node21.html">2.6.1 Changing Instance Attributes</a>
+</ul>
+</ul>
+<LI><A href="zeo.html">3 ZEO</a>
+<UL>
+<LI><A href="node23.html">3.1 How ZEO Works</a>
+<LI><A href="node24.html">3.2 Installing ZEO</a>
+<UL>
+<LI><A href="node25.html">3.2.1 Requirements</a>
+<LI><A href="node26.html">3.2.2 Installation</a>
+</ul>
+<LI><A href="node27.html">3.3 Configuring and Running a ZEO Server</a>
+<LI><A href="node28.html">3.4 Testing the ZEO Installation</a>
+<LI><A href="node29.html">3.5 ZEO Programming Notes</a>
+<LI><A href="node30.html">3.6 Sample Application: chatter.py</a>
+</ul>
+<LI><A href="node31.html">4 Transactions and Versioning</a>
+<UL>
+<LI><A href="node32.html">4.1 Subtransactions</a>
+<LI><A href="node33.html">4.2 Undoing Changes</a>
+<LI><A href="node34.html">4.3 Versions</a>
+<LI><A href="node35.html">4.4 Multithreaded ZODB Programs</a>
+</ul>
+<LI><A href="node36.html">5 Related Modules</a>
+<UL>
+<LI><A href="node37.html">5.1 <tt class="module">ZODB.PersistentMapping</tt></a>
+<LI><A href="node38.html">5.2 <tt class="module">ZODB.PersistentList</tt></a>
+<LI><A href="node39.html">5.3 B-tree Modules</a>
+</ul>
+<LI><A href="node40.html">A. Resources</a>
+<LI><A href="node41.html">B. GNU Free Documentation License</a>
+<UL>
+<LI><A href="node42.html">Preamble</a>
+<LI><A href="node43.html">B..1 Applicability and Definitions</a>
+<LI><A href="node44.html">B..2 Verbatim Copying</a>
+<LI><A href="node45.html">B..3 Copying in Quantity</a>
+<LI><A href="node46.html">B..4 Modifications</a>
+<LI><A href="node47.html">B..5 Combining Documents</a>
+<LI><A href="node48.html">B..6 Collections of Documents</a>
+<LI><A href="node49.html">B..7 Aggregation With Independent Works</a>
+<LI><A href="node50.html">B..8 Translation</a>
+<LI><A href="node51.html">B..9 Termination</a>
+<LI><A href="node52.html">B..10 Future Revisions of This Licence</a>
+<LI><A href="node53.html">ADDENDUM: How to use this License for your documents</a>
+</ul>
+<LI><A href="about.html">About this document ...</a>
+</ul>
+<!--End of Table of Child-Links-->
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><A href="contents.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Next:</b> <a class="sectref" href="contents.html">Contents</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node10.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>2.1.1 Requirements</title>
+<META NAME="description" CONTENT="2.1.1 Requirements">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node11.html">
+<LINK REL="previous" HREF="node9.html">
+<LINK REL="up" HREF="node9.html">
+<LINK REL="next" HREF="node11.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node9.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node9.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node11.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node9.html">2.1 Installing ZODB</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node9.html">2.1 Installing ZODB</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node11.html">2.1.2 Installing the Packages</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H3><A NAME="SECTION000311000000000000000">
+2.1.1 Requirements</A>
+</H3>
+
+<P>
+You'll need Python, of course; version 1.5.2 works with some fixes,
+and it also works with Python 2.0, which is what I primarily use.
+
+<P>
+The code is packaged using Distutils, the new distribution tools for
+Python introduced in Python 2.0.  If you're using 1.5.2, first you'll
+have to get the latest Distutils release from the Distutils SIG page
+at <a class="url" href="http://www.python.org/sigs/distutils-sig/download.html">http://www.python.org/sigs/distutils-sig/download.html</a> and
+install it.  This is simply a matter of untarring or unzipping the
+release package, and then running <code>python setup.py install</code>.
+
+<P>
+If you're using 1.5.2 and have installed previous versions of the
+Distutils, be sure to get the very latest version, since developing
+the ZODB distribution turned up some bugs along the way.  If you
+encounter problems compiling <span class="file">ZODB/TimeStamp.c</span> or your compiler reports
+an error like ``Can't create build/temp.linux2/ExtensionClass.o: No
+such file or directory'', you need an updated version.  Old versions of
+Distutils have two bugs which affect the setup scripts.  First, for a
+long time the <code>define_macros</code> keyword in setup.py files didn't work due
+to a Distutils bug, so I hacked TimeStamp.c in earlier releases.  The
+Distutils have since been fixed, and the hack became unnecessary, so I
+removed it.  Second, the code that creates directories tries to be
+smart and caches them to save time by not trying to create a directory
+twice, but this code was broken in old versions.
+
+<P>
+You'll need a C compiler to build the packages, because there are
+various C extension modules.  At the moment no one is making Windows
+binaries available, so you'll need a Windows development environment to use the 
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node9.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node9.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node11.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node9.html">2.1 Installing ZODB</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node9.html">2.1 Installing ZODB</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node11.html">2.1.2 Installing the Packages</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node11.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>2.1.2 Installing the Packages</title>
+<META NAME="description" CONTENT="2.1.2 Installing the Packages">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="previous" HREF="node10.html">
+<LINK REL="up" HREF="node9.html">
+<LINK REL="next" HREF="node12.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node10.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node9.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node12.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node10.html">2.1.1 Requirements</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node9.html">2.1 Installing ZODB</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node12.html">2.2 How ZODB Works</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H3><A NAME="SECTION000312000000000000000">
+2.1.2 Installing the Packages</A>
+</H3>
+
+<P>
+Download the ZODB tarball containing all the packages for both ZODB
+and ZEO from <a class="url" href="http://www.amk.ca/files/zodb/">http://www.amk.ca/files/zodb/</a>.
+
+<P>
+To build the packages, you must go into the individual directories and
+build and install them one by one.  They should be built and installed
+in this order:
+
+<P>
+
+<OL>
+<LI><code>zodb-basic</code>
+</LI>
+<LI>ExtensionClass
+</LI>
+<LI>ZODB
+</LI>
+<LI><code>BTree</code> and <code>BTrees</code>
+</LI>
+<LI>ZEO
+</LI>
+</OL>
+
+<P>
+In particular, you must install ExtensionClass before building the
+ZODB package; otherwise, the compilation in the ZODB package will die
+complaining that it can't find ExtensionClass.h.  You can manually
+hack the #include path to make it work without installing
+ExtensionClass first, but that's a bit hackish.
+
+<P>
+If you encounter any problems, please let me know at
+<span class="email">akuchlin@mems-exchange.org</span>.
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node10.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node9.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node12.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node10.html">2.1.1 Requirements</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node9.html">2.1 Installing ZODB</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node12.html">2.2 How ZODB Works</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node12.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>2.2 How ZODB Works</title>
+<META NAME="description" CONTENT="2.2 How ZODB Works">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node13.html">
+<LINK REL="previous" HREF="node9.html">
+<LINK REL="up" HREF="node8.html">
+<LINK REL="next" HREF="node13.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node11.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node8.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node13.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node11.html">2.1.2 Installing the Packages</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node8.html">2 ZODB Programming</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node13.html">2.3 Opening a ZODB</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000320000000000000000">
+2.2 How ZODB Works</A>
+</H2>
+
+<P>
+The ZODB is conceptually simple.  Python classes subclass a 
+<tt class="class">Persistent</tt> class to become ZODB-aware. 
+Instances of persistent objects are brought in from a permanent
+storage medium, such as a disk file, when the program needs them, and
+remain cached in RAM.  The ZODB traps modifications to objects, so
+that when a statement such as <code>obj.size = 1</code> is executed, the
+modified object is marked as ``dirty''.  On request, any dirty objects
+are written out to permanent storage; this is called committing a
+transaction.  Transactions can also be aborted or rolled back, which
+results in any changes being discarded, dirty objects reverting to
+their initial state before the transaction began.
+
+<P>
+The term ``transaction'' has a specific technical meaning in computer
+science.  It's extremely important that the contents of a database
+don't get corrupted by software or hardware crashes, and most database
+software offers protection against such corruption by supporting four
+useful properties, Atomicity, Consistency, Isolation, and Durability.
+In computer science jargon these four terms are collectively dubbed
+the ACID properties, forming an acronym from their names.  The
+definitions of the ACID properties are:
+
+<P>
+<DL COMPACT>
+<DT>Atomicity</DT>
+<DD>means that any changes to data made during a transaction 
+are all-or-nothing.  Either all the changes are applied, or none of
+them are.  If a program makes a bunch of modifications and then
+crashes, the database won't be partially modified, potentially leaving
+the data in an inconsistent state; instead all the changes will be
+forgotten.  That's bad, but it's better than having a
+partially-applied modification put the database into an inconsistent
+state.
+
+<P>
+</DD>
+<DT>Consistency</DT>
+<DD>means that the data cannot be placed into a
+logically invalid state; sanity checks can be written and enforced.
+Usually this is done by defining a database schema, and requiring the
+data always matches the schema.  For example, this might enforce that
+the <code>order_number</code> attribute is always an integer, and not a
+string, tuple, or other object.
+
+<P>
+</DD>
+<DT>Isolation</DT>
+<DD>means that two programs or threads running in two
+ different transactions cannot see each other's changes until they
+ commit their transactions.
+
+<P>
+</DD>
+<DT>Durability</DT>
+<DD>means that once a transaction has been committed,
+a subsequent crash will not cause any data to be lost or corrupted.
+
+<P>
+</DD>
+</DL>
+
+<P>
+The ZODB provides 3 of the ACID properties.  Only Consistency is not
+supported; the ZODB has no notion of a database schema, and therefore
+has no way of enforcing consistency with a schema.
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node11.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node8.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node13.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node11.html">2.1.2 Installing the Packages</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node8.html">2 ZODB Programming</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node13.html">2.3 Opening a ZODB</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node13.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>2.3 Opening a ZODB</title>
+<META NAME="description" CONTENT="2.3 Opening a ZODB">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node14.html">
+<LINK REL="previous" HREF="node12.html">
+<LINK REL="up" HREF="node8.html">
+<LINK REL="next" HREF="node14.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node12.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node8.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node14.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node12.html">2.2 How ZODB Works</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node8.html">2 ZODB Programming</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node14.html">2.4 Writing a Persistent</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000330000000000000000">
+2.3 Opening a ZODB</A>
+</H2>
+
+<P>
+There are 3 main interfaces supplied by the ZODB:
+<tt class="class">Storage</tt>, <tt class="class">DB</tt>, and <tt class="class">Connection</tt> classes. The
+<tt class="class">DB</tt> and <tt class="class">Connection</tt> interfaces both have single
+implementations, but there are several different classes that
+implement the <tt class="class">Storage</tt> interface.
+
+<P>
+
+<UL>
+<LI><tt class="class">Storage</tt> classes are the lowest layer, and handle
+ storing and retrieving objects from some form of long-term storage.
+ A few different types of Storage have been written, such as
+ <tt class="class">FileStorage</tt>, which uses regular disk files, and
+ <tt class="class">BerkeleyStorage</tt>, which uses Sleepycat Software's BerkeleyDB
+ database.  You could write a new Storage that stored objects in a
+ relational database or Metakit file, for example, if that would
+ better suit your application.  Two example storages,
+ <tt class="class">DemoStorage</tt> and <tt class="class">MappingStorage</tt>, are available to use
+ as models if you want to write a new Storage.
+
+<P>
+</LI>
+<LI>The <tt class="class">DB</tt> class sits on top of a storage, and mediates the
+ interaction between several connections.  One <tt class="class">DB</tt> instance is
+ created per process.
+
+<P>
+</LI>
+<LI>Finally, the <tt class="class">Connection</tt> class caches objects, and moves
+ them into and out of object storage.  A multi-threaded program can
+ open a separate <tt class="class">Connection</tt> instance for each thread.
+ Different threads can then modify objects and commit their
+ modifications independently.
+
+<P>
+</LI>
+</UL>
+
+<P>
+Preparing to use a ZODB requires 3 steps: you have to open the
+<tt class="class">Storage</tt>, then create a <tt class="class">DB</tt> instance that uses the <tt class="class">Storage</tt>, and then get
+a <tt class="class">Connection</tt> from the <tt class="class">DB instance</tt>.  All this is only a few lines of
+code:
+
+<P>
+<dl><dd><pre class="verbatim">
+from ZODB import FileStorage, DB
+
+storage = FileStorage.FileStorage('/tmp/test-filestorage.fs')
+db = DB(storage)
+conn = db.open()
+</pre></dl>
+
+<P>
+Note that you can use a completely different data storage mechanism by
+changing the first line that opens a <tt class="class">Storage</tt>; the above example uses a
+<tt class="class">FileStorage</tt>.  In section&nbsp;<A href="zeo.html#zeo">3</A>, ``How ZEO Works'',
+you'll see how ZEO uses this flexibility to good effect.
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node12.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
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+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node12.html">2.2 How ZODB Works</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node8.html">2 ZODB Programming</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node14.html">2.4 Writing a Persistent</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node14.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>2.4 Writing a Persistent Class</title>
+<META NAME="description" CONTENT="2.4 Writing a Persistent Class">
+<META NAME="keywords" CONTENT="zodb">
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+
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+<LINK REL="previous" HREF="node13.html">
+<LINK REL="up" HREF="node8.html">
+<LINK REL="next" HREF="node15.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node13.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
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+<td><A HREF="node15.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
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+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node13.html">2.3 Opening a ZODB</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node8.html">2 ZODB Programming</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node15.html">2.5 Rules for Writing</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000340000000000000000">
+2.4 Writing a Persistent Class</A>
+</H2>
+
+<P>
+Making a Python class persistent is quite simple; it simply needs to
+subclass from the <tt class="class">Persistent</tt> class, as shown in this example:
+
+<P>
+<dl><dd><pre class="verbatim">
+import ZODB
+from Persistence import Persistent
+
+class User(Persistent):
+    pass
+</pre></dl>
+
+<P>
+The apparently unnecessary <code>import ZODB</code> statement is
+needed for the following <code>from...import</code> statement to work
+correctly, since the ZODB code does some magical tricks with
+importing.
+
+<P>
+For simplicity, in the examples the <tt class="class">User</tt> class will
+simply be used as a holder for a bunch of attributes.  Normally the
+class would define various methods that add functionality, but that
+has no impact on the ZODB's treatment of the class.
+
+<P>
+The ZODB uses persistence by reachability; starting from a set of root
+objects, all the attributes of those objects are made persistent,
+whether they're simple Python data types or class instances.  There's
+no method to explicitly store objects in a ZODB database; simply
+assign them as an attribute of an object, or store them in a mapping,
+that's already in the database.  This chain of containment must
+eventually reach back to the root object of the database.
+
+<P>
+As an example, we'll create a simple database of users that allows
+retrieving a <tt class="class">User</tt> object given the user's ID.  First, we
+retrieve the primary root object of the ZODB using the <tt class="method">root()</tt>
+method of the <tt class="class">Connection</tt> instance.  The root object behaves
+like a Python dictionary, so you can just add a new key/value pair for
+your application's root object.  We'll insert a <tt class="class">BTree</tt> object
+that will contain all the <tt class="class">User</tt> objects.  (The
+<tt class="class">BTree</tt> module is also included as part of Zope.)
+
+<P>
+<dl><dd><pre class="verbatim">
+dbroot = conn.root()
+
+# Ensure that a 'userdb' key is present 
+# in the root
+if not dbroot.has_key('userdb'):
+    import BTree
+    dbroot['userdb'] = BTree.BTree()
+
+userdb = dbroot['userdb']
+</pre></dl>
+
+<P>
+Inserting a new user is simple: create the <tt class="class">User</tt> object, fill
+it with data, insert it into the <tt class="class">BTree</tt> instance, and commit
+this transaction.
+
+<P>
+<dl><dd><pre class="verbatim"># Create new User instance
+newuser = User() 
+
+# Add whatever attributes you want to track
+newuser.id = 'amk' 
+newuser.first_name = 'Andrew' ; newuser.last_name = 'Kuchling'
+...
+
+# Add object to the BTree, keyed on the ID
+userdb[newuser.id] = newuser
+
+# Commit the change
+get_transaction().commit()
+</pre></dl>
+
+<P>
+When you import the ZODB package, it adds a new function,
+<tt class="function">get_transaction()</tt>, to Python's collection of built-in
+functions.  <tt class="function">get_transaction()</tt> returns a <tt class="class">Transaction</tt>
+object, which has two important methods: <tt class="method">commit()</tt> and
+<tt class="method">abort()</tt>.  <tt class="method">commit()</tt> writes any modified objects
+to disk, making the changes permanent, while <tt class="method">abort()</tt> rolls
+back any changes that have been made, restoring the original state of
+the objects.  If you're familiar with database transactional
+semantics, this is all what you'd expect.
+
+<P>
+Because the integration with Python is so complete, it's a lot like
+having transactional semantics for your program's variables, and you
+can experiment with transactions at the Python interpreter's prompt:
+
+<P>
+<dl><dd><pre class="verbatim">&gt;&gt;&gt; newuser
+&lt;User instance at 81b1f40&gt;
+&gt;&gt;&gt; newuser.first_name           # Print initial value
+'Andrew'         
+&gt;&gt;&gt; newuser.first_name = 'Bob'   # Change first name
+&gt;&gt;&gt; newuser.first_name           # Verify the change
+'Bob'
+&gt;&gt;&gt; get_transaction().abort()    # Abort transaction
+&gt;&gt;&gt; newuser.first_name           # The value has changed back
+'Andrew'
+</pre></dl>
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node13.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node8.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
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+<td><A HREF="node15.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
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+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node13.html">2.3 Opening a ZODB</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node8.html">2 ZODB Programming</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node15.html">2.5 Rules for Writing</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node15.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>2.5 Rules for Writing Persistent Classes</title>
+<META NAME="description" CONTENT="2.5 Rules for Writing Persistent Classes">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
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+
+<LINK REL="next" HREF="node20.html">
+<LINK REL="previous" HREF="node14.html">
+<LINK REL="up" HREF="node8.html">
+<LINK REL="next" HREF="node16.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node14.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node8.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
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+<td><A HREF="node16.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node14.html">2.4 Writing a Persistent</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node8.html">2 ZODB Programming</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node16.html">2.5.1 Modifying Mutable Objects</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000350000000000000000">
+2.5 Rules for Writing Persistent Classes</A>
+</H2>
+
+<P>
+Practically all persistent languages impose some restrictions on
+programming style, warning against constructs they can't handle or
+adding subtle semantic changes, and the ZODB is no exception.
+Happily, the ZODB's restrictions are fairly simple to understand, and
+in practice it isn't too painful to work around them.
+
+<P>
+The summary of rules is as follows:
+
+<P>
+
+<UL>
+<LI>If you modify a mutable object that's the value of an object's
+attribute, the ZODB can't catch that, and won't mark the object as
+dirty.  
+The solution is to either set the dirty bit yourself when you modify
+mutable objects, or use a wrapper for Python's lists and dictionaries
+(<tt class="class">PersistentList</tt>, 
+<tt class="class">PersistentMapping</tt>)
+that will set the dirty bit properly.
+
+<P>
+</LI>
+<LI>Certain of Python's special methods don't work when they're
+defined on ExtensionClasses.  The most important ones are the
+<tt class="method">__cmp__</tt> method, and the reversed versions of binary
+arithmetic operations: <tt class="method">__radd__</tt>, <tt class="method">__rsub__</tt>, and so
+forth.
+
+<P>
+</LI>
+<LI>Python's built-in <tt class="function">isinstance()</tt> and <tt class="function">issubclass()</tt>
+functions don't work properly on ExtensionClasses.  Solution: use
+custom <tt class="function">isinstance()</tt> and <tt class="function">issubclass()</tt> functions
+that handle ExtensionClasses correctly.
+
+<P>
+</LI>
+<LI>Recent versions of the ZODB allow writing a class with 
+<tt class="method">__setattr__</tt> , <tt class="method">__getattr__</tt>, or <tt class="method">__delattr__</tt> methods.  (Older versions didn't support this at all.)
+If you write such a <tt class="method">__setattr__</tt> or <tt class="method">__delattr__</tt> method, 
+its code has to set the dirty bit manually, 
+
+<P>
+</LI>
+</UL>
+
+<P>
+Let's look at each of these rules in detail.
+
+<P>
+
+<p><hr>
+<!--Table of Child-Links-->
+<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a>
+
+<UL>
+<LI><A href="node16.html">2.5.1 Modifying Mutable Objects</a>
+<LI><A href="node17.html">2.5.2 Some Special Methods Don't Work</a>
+<LI><A href="node18.html">2.5.3 Fixing <tt class="function">isinstance</tt> and <tt class="function">issubclass</tt></a>
+<LI><A href="node19.html">2.5.4 <tt class="method">__getattr__</tt>, <tt class="method">__delattr__</tt>, and <tt class="method">__setattr__</tt></a>
+</ul>
+<!--End of Table of Child-Links-->
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node14.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node8.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node16.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node14.html">2.4 Writing a Persistent</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node8.html">2 ZODB Programming</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node16.html">2.5.1 Modifying Mutable Objects</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node16.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>2.5.1 Modifying Mutable Objects</title>
+<META NAME="description" CONTENT="2.5.1 Modifying Mutable Objects">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
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+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node17.html">
+<LINK REL="previous" HREF="node15.html">
+<LINK REL="up" HREF="node15.html">
+<LINK REL="next" HREF="node17.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node15.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
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+<td><A HREF="node15.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node17.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node15.html">2.5 Rules for Writing</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node15.html">2.5 Rules for Writing</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node17.html">2.5.2 Some Special Methods</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H3><A NAME="SECTION000351000000000000000">
+2.5.1 Modifying Mutable Objects</A>
+</H3>
+
+<P>
+The ZODB uses various Python hooks to catch attribute accesses, and
+can trap most of the ways of modifying an object, but not all of them.
+If you modify a <tt class="class">User</tt> object by assigning to one of its
+attributes, as in <code>userobj.first_name = 'Andrew'</code>, the ZODB will
+mark the object as having been changed, and it'll be written out on
+the following <tt class="method">commit()</tt>.
+
+<P>
+The most common idiom that <i>isn't</i> caught by the ZODB is
+mutating a list or dictionary.  If <tt class="class">User</tt> objects have a
+attribute named <code>friends</code> containing a list, calling
+<code>userobj.friends.append(otherUser)</code> doesn't mark
+<code>userobj</code> as modified; from the ZODB's point of
+view, <code>userobj.friends</code> was only read, and its value, which
+happened to be an ordinary Python list, was returned.  The ZODB isn't
+aware that the object returned was subsequently modified.
+
+<P>
+This is one of the few quirks you'll have to remember when using the
+ZODB; if you modify a mutable attribute of an object in place, you
+have to manually mark the object as having been modified by setting
+its dirty bit to true.  This is done by setting the
+<tt class="member">_p_changed</tt> attribute of the object to true:
+
+<P>
+<dl><dd><pre class="verbatim">
+userobj.friends.append(otherUser)
+userobj._p_changed = 1
+</pre></dl>
+
+<P>
+An obsolete way of doing this that's still supported is calling the
+<tt class="method">__changed__()</tt> method instead, but setting <tt class="member">_p_changed</tt> 
+is the preferred way.
+
+<P>
+You can hide the implementation detail of having to mark objects as
+dirty by designing your class's API to not use direct attribute
+access; instead, you can use the Java-style approach of accessor
+methods for everything, and then set the dirty bit within the accessor
+method.  For example, you might forbid accessing the <code>friends</code>
+attribute directly, and add a <tt class="method">get_friend_list()</tt> accessor and
+an <tt class="method">add_friend()</tt> modifier method to the class.  <tt class="method">add_friend()</tt>
+would then look like this:
+
+<P>
+<dl><dd><pre class="verbatim">
+    def add_friend(self, friend):
+        self.friends.append(otherUser)
+        self._p_changed = 1
+</pre></dl>
+
+<P>
+Alternatively, you could use a ZODB-aware list or mapping type that
+handles the dirty bit for you.  The ZODB comes with a
+<tt class="class">PersistentMapping</tt> class, and I've contributed a
+<tt class="class">PersistentList</tt> class that's included in my ZODB distribution, 
+and may make it into a future upstream release of Zope.
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node15.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node15.html"><img src="/python/writing/icons/up.gif"
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+<td><A HREF="node17.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node15.html">2.5 Rules for Writing</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node15.html">2.5 Rules for Writing</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node17.html">2.5.2 Some Special Methods</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node17.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>2.5.2 Some Special Methods Don't Work</title>
+<META NAME="description" CONTENT="2.5.2 Some Special Methods Don't Work">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node18.html">
+<LINK REL="previous" HREF="node16.html">
+<LINK REL="up" HREF="node15.html">
+<LINK REL="next" HREF="node18.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node16.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node15.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node18.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node16.html">2.5.1 Modifying Mutable Objects</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node15.html">2.5 Rules for Writing</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node18.html">2.5.3 Fixing isinstance and</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H3><A NAME="SECTION000352000000000000000">
+2.5.2 Some Special Methods Don't Work</A>
+</H3>
+
+<P>
+Don't bother defining certain special methods on
+ExtensionClasses, because they won't work.  Most notably, the
+<tt class="method">__cmp__</tt> method on an ExtensionClass will never be called.
+Neither will the reversed versions of binary arithmetic operations,
+such as <tt class="method">__radd__</tt> and <tt class="method">__rsub__</tt>.
+
+<P>
+This is a moderately annoying limitation.  It means that the
+<tt class="class">PersistentList</tt> class can't implement comparisons with regular
+sequence objects, and therefore statements such as 
+<code>if perslist==[]</code> don't do what you expect; instead of performing the correct
+comparison, they return some arbitrary fixed result, so the <code>if</code>
+statement will always be true or always be false.  There is no good
+solution to this problem at the moment, so all you can do is design
+class interfaces that don't need to overload
+<tt class="method">__cmp__</tt> or the <tt class="method">__r*__</tt> methods.
+
+<P>
+This limitation is mostly Python's fault.  As of Python 2.1, the most
+recent version at this writing, the code which handles comparing two
+Python objects contains a hard-wired check for objects that are class
+instances, which means that <code>type(obj) == types.InstanceType</code>.
+The code inside the Python interpreter looks like this:
+
+<P>
+<dl><dd><pre class="verbatim">
+/* Code to compare objects v and w */
+if (PyInstance_Check(v) || PyInstance_Check(w))
+        return PyInstance_DoBinOp(v, w, "__cmp__", "__rcmp__", do_cmp);
+/* Do usual Python comparison of v,w */
+c = PyObject_Compare(v, w);
+</pre></dl>
+
+<P>
+While ExtensionClasses try to behave as much like regular Python
+instances as possible, they are still not instances, and
+<tt class="function">type()</tt> doesn't return the <code>InstanceType</code> object, so 
+no attempt is ever made to call <tt class="method">__cmp__</tt>.  Perhaps Python 2.2
+will repair this.
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node16.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node15.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node18.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node16.html">2.5.1 Modifying Mutable Objects</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node15.html">2.5 Rules for Writing</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node18.html">2.5.3 Fixing isinstance and</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node18.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>2.5.3 Fixing isinstance and issubclass</title>
+<META NAME="description" CONTENT="2.5.3 Fixing isinstance and issubclass">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node19.html">
+<LINK REL="previous" HREF="node17.html">
+<LINK REL="up" HREF="node15.html">
+<LINK REL="next" HREF="node19.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node17.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node15.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node19.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node17.html">2.5.2 Some Special Methods</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node15.html">2.5 Rules for Writing</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node19.html">2.5.4 __getattr__, __delattr__, and</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H3><A NAME="SECTION000353000000000000000">
+2.5.3 Fixing <tt class="function">isinstance</tt> and <tt class="function">issubclass</tt></A>
+</H3>
+
+<P>
+Python's built-in functions 
+<tt class="function">isinstance()</tt> and <tt class="function">issubclass</tt> don't
+work on ExtensionClass instances, for much the same reason that 
+<tt class="method">__cmp__</tt> is never called; in some bits of the Python core code,
+branches are taken only if an object is of the <tt class="class">InstanceType</tt>
+type, and this can never be true for an ExtensionClass instance.
+Python 2.1 tried to fix this, and changed these functions slightly in
+an effort to make them work for ExtensionClasses; unfortunately, the
+changes didn't work.
+
+<P>
+The solution is to use customized versions of these functions that
+handle ExtensionClasses specially and fall back to the built-in
+version otherwise.  Here are the versions we've written at the MEMS Exchange:
+
+<P>
+<dl><dd><pre class="verbatim">
+# The built-in 'isinstance()' and 'issubclass()' won't work on
+# ExtensionClasses, so you have to use the versions supplied here.
+# (But those versions work fine on regular instances and classes too,
+# so you should *always* use them.)
+
+def issubclass (class1, class2):
+    """A version of 'issubclass' that works with extension classes
+    as well as regular Python classes.
+    """
+
+    # Both class objects are regular Python classes, so use the
+    # built-in 'issubclass()'.
+    if type(class1) is ClassType and type(class2) is ClassType:
+        return __builtin__.issubclass(class1, class2)
+
+    # Both so-called class objects have a '__bases__' attribute: ie.,
+    # they aren't regular Python classes, but they sure look like them.
+    # Assume they are extension classes and reimplement what the builtin
+    # 'issubclass()' does behind the scenes.
+    elif hasattr(class1, '__bases__') and hasattr(class2, '__bases__'):
+        # XXX it appears that "ec.__class__ is type(ec)" for an
+        # extension class 'ec': could we/should we use this as an
+        # additional check for extension classes?
+
+        # Breadth-first traversal of class1's superclass tree.  Order
+        # doesn't matter because we're just looking for a "yes/no"
+        # answer from the tree; if we were trying to resolve a name,
+        # order would be important!
+        stack = [class1]
+        while stack:
+            if stack[0] is class2:
+                return 1
+            stack.extend(list(stack[0].__bases__))
+            del stack[0]
+        else:
+            return 0
+
+    # Not a regular class, not an extension class: blow up for consistency
+    # with builtin 'issubclass()"
+    else:
+        raise TypeError, "arguments must be class or ExtensionClass objects"
+
+# issubclass ()
+
+def isinstance (object, klass):
+    """A version of 'isinstance' that works with extension classes
+    as well as regular Python classes."""
+
+    if type(klass) is TypeType:
+        return __builtin__.isinstance(object, klass)
+    elif hasattr(object, '__class__'):
+        return issubclass(object.__class__, klass)
+    else:
+        return 0
+</pre></dl>
+
+<P>
+I'd recommend putting these functions in a module that always gets
+imported.  The convention on my work project is to put them in
+<span class="file">mems/lib/base.py</span>, which contains various fundamental classes
+and functions for our system, and access them like this:
+
+<P>
+<dl><dd><pre class="verbatim">
+from mems.lib import base
+...
+if base.isinstance(object, Class): ...
+</pre></dl>
+
+<P>
+Don't insert the modified functions into Python's
+<tt class="module">__builtin__</tt> module, or import just the
+<tt class="function">isinstance()</tt> and <tt class="function">issubclass</tt> functions.  
+If you consistently use <tt class="function">base.isinstance()</tt>, then forgetting
+to import the <tt class="module">base</tt> module will result in a
+<tt class="exception">NameError</tt> exception.  In the
+case of a forgotten import, calling the functions directly would use
+Python's built-in versions, leading to subtle bugs that might not be
+noticed for some time.
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node17.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node15.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
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+<td><A HREF="node19.html"><img src="/python/writing/icons/next.gif"
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+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node17.html">2.5.2 Some Special Methods</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node15.html">2.5 Rules for Writing</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node19.html">2.5.4 __getattr__, __delattr__, and</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node19.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>2.5.4 __getattr__, __delattr__, and __setattr__</title>
+<META NAME="description" CONTENT="2.5.4 __getattr__, __delattr__, and __setattr__">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="previous" HREF="node18.html">
+<LINK REL="up" HREF="node15.html">
+<LINK REL="next" HREF="node20.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node18.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node15.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node20.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node18.html">2.5.3 Fixing isinstance and</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node15.html">2.5 Rules for Writing</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node20.html">2.6 Writing Persistent Classes</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H3><A NAME="SECTION000354000000000000000">
+2.5.4 <tt class="method">__getattr__</tt>, <tt class="method">__delattr__</tt>, and <tt class="method">__setattr__</tt></A>
+</H3>
+
+<P>
+Recent versions of ZODB allow writing persistent classes that have
+<tt class="method">__getattr__</tt>, <tt class="method">__delattr__</tt>, or <tt class="method">__setattr__</tt>
+methods.  The one minor complication is that the machinery for
+automatically detecting changes to the object is disabled while the
+<tt class="method">__getattr__</tt>, <tt class="method">__delattr__</tt>, or <tt class="method">__setattr__</tt>
+method is executing.  This means that if the object is modified, the
+object should be marked as dirty by setting the object's
+<tt class="member">_p_changed</tt> method to true.
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node18.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node15.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node20.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node18.html">2.5.3 Fixing isinstance and</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node15.html">2.5 Rules for Writing</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node20.html">2.6 Writing Persistent Classes</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node2.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>1 Introduction</title>
+<META NAME="description" CONTENT="1 Introduction">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node8.html">
+<LINK REL="previous" href="contents.html">
+<LINK REL="up" HREF="zodb.html">
+<LINK REL="next" HREF="node3.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A href="contents.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="zodb.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node3.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" href="contents.html">Contents</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="zodb.html">ZODB/ZEO Programming Guide</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node3.html">1.1 What is the</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H1><A NAME="SECTION000200000000000000000">
+1 Introduction</A>
+</H1>
+
+<P>
+This guide explains how to write Python programs that use the Z Object
+Database (ZODB) and Zope Enterprise Objects (ZEO).  The latest version
+of the guide is always available at
+<a class="url" href="http://www.amk.ca/zodb/guide/">http://www.amk.ca/zodb/guide/</a>.
+
+<P>
+
+<p><hr>
+<!--Table of Child-Links-->
+<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a>
+
+<UL>
+<LI><A href="node3.html">1.1 What is the ZODB?</a>
+<LI><A href="node4.html">1.2 OODBs vs. Relational DBs</a>
+<LI><A href="node5.html">1.3 What is ZEO?</a>
+<LI><A href="node6.html">1.4 About this guide</a>
+<LI><A href="node7.html">1.5 Acknowledgements</a>
+</ul>
+<!--End of Table of Child-Links-->
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A href="contents.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="zodb.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node3.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" href="contents.html">Contents</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="zodb.html">ZODB/ZEO Programming Guide</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node3.html">1.1 What is the</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node20.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>2.6 Writing Persistent Classes</title>
+<META NAME="description" CONTENT="2.6 Writing Persistent Classes">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="previous" HREF="node15.html">
+<LINK REL="up" HREF="node8.html">
+<LINK REL="next" HREF="node21.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node19.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node8.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node21.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node19.html">2.5.4 __getattr__, __delattr__, and</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node8.html">2 ZODB Programming</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node21.html">2.6.1 Changing Instance Attributes</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000360000000000000000">
+2.6 Writing Persistent Classes</A>
+</H2>
+
+<P>
+Now that we've looked at the basics of programming using the ZODB,
+we'll turn to some more subtle tasks that are likely to come up for
+anyone using the ZODB in a production system.
+
+<P>
+
+<p><hr>
+<!--Table of Child-Links-->
+<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a>
+
+<UL>
+<LI><A href="node21.html">2.6.1 Changing Instance Attributes</a>
+</ul>
+<!--End of Table of Child-Links-->
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node19.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node8.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node21.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node19.html">2.5.4 __getattr__, __delattr__, and</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node8.html">2 ZODB Programming</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node21.html">2.6.1 Changing Instance Attributes</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node21.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>2.6.1 Changing Instance Attributes</title>
+<META NAME="description" CONTENT="2.6.1 Changing Instance Attributes">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="previous" HREF="node20.html">
+<LINK REL="up" HREF="node20.html">
+<LINK REL="next" href="zeo.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node20.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node20.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A href="zeo.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node20.html">2.6 Writing Persistent Classes</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node20.html">2.6 Writing Persistent Classes</A>
+<b class="navlabel">Next:</b> <a class="sectref" href="zeo.html">3 ZEO</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H3><A NAME="SECTION000361000000000000000">
+2.6.1 Changing Instance Attributes</A>
+</H3>
+
+<P>
+Ideally, before making a class persistent you would get its interface
+right the first time, so that no attributes would ever need to be
+added, removed, or have their interpretation change over time.  It's a
+worthy goal, but also an impractical one unless you're gifted with
+perfect knowledge of the future.  Such unnatural foresight can't be
+required of any person, so you therefore have to be prepared to handle
+such structural changes gracefully.  In object-oriented database
+terminology, this is a schema update.  The ZODB doesn't have an actual
+schema specification, but you're changing the software's expectations
+of the data contained by an object, so you're implicitly changing the
+schema.
+
+<P>
+One way to handle such a change is to write a one-time conversion
+program that will loop over every single object in the database and
+update them to match the new schema.  This can be easy if your network
+of object references is quite structured, making it easy to find all
+the instances of the class being modified.  For example, if all
+<tt class="class">User</tt> objects can be found inside a single dictionary or
+B-tree, then it would be a simple matter to loop over every
+<tt class="class">User</tt> instance with a <tt class="keyword">for</tt> statement.
+This is more difficult if your object graph is less structured; if
+<tt class="class">User</tt> objects can be found as attributes of any number of
+different class instances, then there's no longer any easy way to find
+them all, short of writing a generalized object traversal function
+that would walk over every single object in a ZODB, checking each one
+to see if it's an instance of <tt class="class">User</tt>.  
+<A NAME="tex2html1"
+  HREF="#foot287"><SUP>1</SUP></A>Some OODBs support a feature called extents, which allow quickly
+finding all the instances of a given class, no matter where they are
+in the object graph; unfortunately the ZODB doesn't offer extents as a
+feature.
+
+<P>
+XXX Rest of section not written yet: __getstate__/__setstate__
+
+<P>
+<BR><HR><H4>Footnotes</H4>
+<DL>
+<DT><A NAME="foot287">...User.  
+</A><A NAME="foot287"
+ HREF="node21.html#tex2html1"><SUP>1</SUP></A>
+<DD>XXX is there a convenience method for walking the object graph hiding
+somewhere inside DC's code?  Should there be a utility method for
+doing this?  Should I write one and include it in this section?
+
+</DL>
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node20.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node20.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A href="zeo.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node20.html">2.6 Writing Persistent Classes</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node20.html">2.6 Writing Persistent Classes</A>
+<b class="navlabel">Next:</b> <a class="sectref" href="zeo.html">3 ZEO</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node23.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>3.1 How ZEO Works</title>
+<META NAME="description" CONTENT="3.1 How ZEO Works">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node24.html">
+<LINK REL="previous" href="zeo.html">
+<LINK REL="up" href="zeo.html">
+<LINK REL="next" HREF="node24.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A href="zeo.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A href="zeo.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node24.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" href="zeo.html">3 ZEO</A>
+<b class="navlabel">Up:</b> <a class="sectref" href="zeo.html">3 ZEO</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node24.html">3.2 Installing ZEO</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000410000000000000000">
+3.1 How ZEO Works</A>
+</H2>
+
+<P>
+The ZODB, as I've described it so far, can only be used within a
+single Python process (though perhaps with multiple threads).  ZEO,
+Zope Enterprise Objects, extends the ZODB machinery to provide access
+to objects over a network.  The name "Zope Enterprise Objects" is a
+bit misleading; ZEO can be used to store Python objects and access
+them in a distributed fashion without Zope ever entering the picture.
+The combination of ZEO and ZODB is essentially a Python-specific
+object database.
+
+<P>
+ZEO consists of about 1400 lines of Python code.  The code is
+relatively small because it contains only code for a TCP/IP server,
+and for a new type of Storage, <tt class="class">ClientStorage</tt>.
+<tt class="class">ClientStorage</tt> doesn't use disk files at all; it simply
+makes remote procedure calls to the server, which then passes them on
+a regular <tt class="class">Storage</tt> class such as <tt class="class">FileStorage</tt>.  The
+following diagram lays out the system:
+
+<P>
+XXX insert diagram here later
+
+<P>
+Any number of processes can create a <tt class="class">ClientStorage</tt>
+instance, and any number of threads in each process can be using that
+instance.  <tt class="class">ClientStorage</tt> aggressively caches objects
+locally, so in order to avoid using stale data, the ZEO server sends
+an invalidate message to all the connected <tt class="class">ClientStorage</tt>
+instances on every write operation.  The invalidate message contains
+the object ID for each object that's been modified, letting the
+<tt class="class">ClientStorage</tt> instances delete the old data for the
+given object from their caches.
+
+<P>
+This design decision has some consequences you should be aware of.
+First, while ZEO isn't tied to Zope, it was first written for use with
+Zope, which stores HTML, images, and program code in the database.  As
+a result, reads from the database are <i>far</i> more frequent than
+writes, and ZEO is therefore better suited for read-intensive
+applications.  If every <tt class="class">ClientStorage</tt> is writing to the
+database all the time, this will result in a storm of invalidate
+messages being sent, and this might take up more processing time than
+the actual database operations themselves.
+
+<P>
+On the other hand, for applications that have few writes in comparison
+to the number of read accesses, this aggressive caching can be a major
+win.  Consider a Slashdot-like discussion forum that divides the load
+among several Web servers.  If news items and postings are represented
+by objects and accessed through ZEO, then the most heavily accessed
+objects - the most recent or most popular postings - will very
+quickly wind up in the caches of the
+<tt class="class">ClientStorage</tt> instances on the front-end servers.  The
+back-end ZEO server will do relatively little work, only being called
+upon to return the occasional older posting that's requested, and to
+send the occasional invalidate message when a new posting is added.
+The ZEO server isn't going to be contacted for every single request,
+so its workload will remain manageable.
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A href="zeo.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A href="zeo.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node24.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" href="zeo.html">3 ZEO</A>
+<b class="navlabel">Up:</b> <a class="sectref" href="zeo.html">3 ZEO</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node24.html">3.2 Installing ZEO</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node24.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>3.2 Installing ZEO</title>
+<META NAME="description" CONTENT="3.2 Installing ZEO">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node27.html">
+<LINK REL="previous" HREF="node23.html">
+<LINK REL="up" href="zeo.html">
+<LINK REL="next" HREF="node25.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node23.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A href="zeo.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node25.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node23.html">3.1 How ZEO Works</A>
+<b class="navlabel">Up:</b> <a class="sectref" href="zeo.html">3 ZEO</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node25.html">3.2.1 Requirements</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000420000000000000000">
+3.2 Installing ZEO</A>
+</H2>
+
+<P>
+This section covers how to install the ZEO package, and how to 
+configure and run a ZEO Storage Server on a machine. 
+
+<P>
+
+<p><hr>
+<!--Table of Child-Links-->
+<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a>
+
+<UL>
+<LI><A href="node25.html">3.2.1 Requirements</a>
+<LI><A href="node26.html">3.2.2 Installation</a>
+</ul>
+<!--End of Table of Child-Links-->
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node23.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A href="zeo.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node25.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node23.html">3.1 How ZEO Works</A>
+<b class="navlabel">Up:</b> <a class="sectref" href="zeo.html">3 ZEO</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node25.html">3.2.1 Requirements</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node25.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>3.2.1 Requirements</title>
+<META NAME="description" CONTENT="3.2.1 Requirements">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node26.html">
+<LINK REL="previous" HREF="node24.html">
+<LINK REL="up" HREF="node24.html">
+<LINK REL="next" HREF="node26.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node24.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node24.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node26.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node24.html">3.2 Installing ZEO</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node24.html">3.2 Installing ZEO</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node26.html">3.2.2 Installation</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H3><A NAME="SECTION000421000000000000000">
+3.2.1 Requirements</A>
+</H3>
+
+<P>
+To run a ZEO server, you'll need Python 1.5.2 or 2.0, and the ZODB
+packages from <a class="url" href="http://www.amk.ca/files/zodb/">http://www.amk.ca/files/zodb/</a>have to be installed.  
+
+<P>
+<i>Note for Python 1.5.2 users</i>: ZEO requires updated versions
+of the <tt class="module">asyncore.py</tt> and <tt class="module">asynchat.py</tt> modules that are
+included in 1.5.2's standard library.  Current versions of the ZODB
+distribution install private versions of these modules, so you
+shouldn't need to grab updated versions yourself.  (The symptom of
+this problem is a traceback on attempting to run a ZEO client program:
+the traceback is ``TypeError: too many arguments; expected 2, got 3''
+around line 100 of <span class="file">smac.py</span>.
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node24.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node24.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node26.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node24.html">3.2 Installing ZEO</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node24.html">3.2 Installing ZEO</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node26.html">3.2.2 Installation</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node26.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>3.2.2 Installation</title>
+<META NAME="description" CONTENT="3.2.2 Installation">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="previous" HREF="node25.html">
+<LINK REL="up" HREF="node24.html">
+<LINK REL="next" HREF="node27.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node25.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node24.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node27.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node25.html">3.2.1 Requirements</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node24.html">3.2 Installing ZEO</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node27.html">3.3 Configuring and Running</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H3><A NAME="SECTION000422000000000000000">
+3.2.2 Installation</A>
+</H3>
+
+<P>
+Installing the ZEO package is easy.  Just run <code>python setup.py
+install</code>.  This will install the ZEO/ package into your Python
+installation, and copy various files into their proper locations:
+<span class="file">zeo.conf</span> will be put into <span class="file">/usr/local/etc/</span>, a <span class="file">zeo</span> startup
+script will be put in <span class="file">/etc/rc.d/init.d/</span>, and the <span class="file">zeod</span>
+daemon program will be placed in <span class="file">/usr/local/bin</span>.
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node25.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node24.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node27.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node25.html">3.2.1 Requirements</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node24.html">3.2 Installing ZEO</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node27.html">3.3 Configuring and Running</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node27.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>3.3 Configuring and Running a ZEO Server</title>
+<META NAME="description" CONTENT="3.3 Configuring and Running a ZEO Server">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node28.html">
+<LINK REL="previous" HREF="node24.html">
+<LINK REL="up" href="zeo.html">
+<LINK REL="next" HREF="node28.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node26.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A href="zeo.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node28.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node26.html">3.2.2 Installation</A>
+<b class="navlabel">Up:</b> <a class="sectref" href="zeo.html">3 ZEO</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node28.html">3.4 Testing the ZEO</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000430000000000000000">
+3.3 Configuring and Running a ZEO Server</A>
+</H2>
+
+<P>
+Edit <code>/usr/local/etc/zeo.conf</code> appropriately for your desired
+setup.  This configuration file controls the port on which ZEO will
+listen for connections, the user and group IDs under which the server
+will be executed, and the location of the concrete <tt class="class">Storage</tt>
+object that will be made network-accessible.
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node26.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A href="zeo.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node28.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node26.html">3.2.2 Installation</A>
+<b class="navlabel">Up:</b> <a class="sectref" href="zeo.html">3 ZEO</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node28.html">3.4 Testing the ZEO</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node28.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>3.4 Testing the ZEO Installation</title>
+<META NAME="description" CONTENT="3.4 Testing the ZEO Installation">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node29.html">
+<LINK REL="previous" HREF="node27.html">
+<LINK REL="up" href="zeo.html">
+<LINK REL="next" HREF="node29.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node27.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A href="zeo.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node29.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node27.html">3.3 Configuring and Running</A>
+<b class="navlabel">Up:</b> <a class="sectref" href="zeo.html">3 ZEO</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node29.html">3.5 ZEO Programming Notes</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000440000000000000000">
+3.4 Testing the ZEO Installation</A>
+</H2>
+
+<P>
+Once a ZEO server is up and running, using it is just like using ZODB
+with a more conventional disk-based storage; no new programming
+details are introduced by using a remote server.  The only difference
+is that programs must create a <tt class="class">ClientStorage</tt> instance instead
+of a <tt class="class">FileStorage</tt> instance.  From that point onward, ZODB-based
+code is happily unaware that objects are being retrieved from a ZEO
+server, and not from the local disk.
+
+<P>
+As an example, and to test whether ZEO is working correctly, try
+running the following lines of code, which will connect to the server,
+add some bits of data to the root of the ZODB, and commits the
+transaction:
+
+<P>
+<dl><dd><pre class="verbatim">
+from ZEO import ClientStorage
+from ZODB import DB
+
+# Change next line to connect to your ZEO server
+addr = ('kronos.example.com', 1975)
+storage = ClientStorage.ClientStorage(addr)
+db = DB(storage)
+conn = db.open()
+root = conn.root()
+
+# Store some things in the root
+root['list'] = ['a', 'b', 1.0, 3]
+root['dict'] = {'a':1, 'b':4}
+
+# Commit the transaction
+get_transaction().commit()
+</pre></dl>
+
+<P>
+If this code runs properly, then your ZEO server is working correctly.
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node27.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A href="zeo.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node29.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node27.html">3.3 Configuring and Running</A>
+<b class="navlabel">Up:</b> <a class="sectref" href="zeo.html">3 ZEO</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node29.html">3.5 ZEO Programming Notes</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node29.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>3.5 ZEO Programming Notes</title>
+<META NAME="description" CONTENT="3.5 ZEO Programming Notes">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node30.html">
+<LINK REL="previous" HREF="node28.html">
+<LINK REL="up" href="zeo.html">
+<LINK REL="next" HREF="node30.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node28.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A href="zeo.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node30.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node28.html">3.4 Testing the ZEO</A>
+<b class="navlabel">Up:</b> <a class="sectref" href="zeo.html">3 ZEO</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node30.html">3.6 Sample Application: chatter.py</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000450000000000000000">
+3.5 ZEO Programming Notes</A>
+</H2>
+
+<P>
+XXX The Connection.sync() method and its necessity (if it works at all!) 
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node28.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A href="zeo.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node30.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node28.html">3.4 Testing the ZEO</A>
+<b class="navlabel">Up:</b> <a class="sectref" href="zeo.html">3 ZEO</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node30.html">3.6 Sample Application: chatter.py</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node3.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>1.1 What is the ZODB?</title>
+<META NAME="description" CONTENT="1.1 What is the ZODB?">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node4.html">
+<LINK REL="previous" HREF="node2.html">
+<LINK REL="up" HREF="node2.html">
+<LINK REL="next" HREF="node4.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node2.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node2.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node4.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node2.html">1 Introduction</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node2.html">1 Introduction</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node4.html">1.2 OODBs vs. Relational</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000210000000000000000">
+1.1 What is the ZODB?</A>
+</H2>
+
+<P>
+The ZODB is a persistence system for Python objects.  Persistent
+programming languages provide facilities that automatically write
+objects to disk and read them in again when they're required by a
+running program.  By installing the ZODB, you add such facilities to
+Python.
+
+<P>
+It's certainly possible to build your own system for making Python
+objects persistent.  The usual starting points are the <tt class="module">pickle</tt>
+module, for converting objects into a string representation, and
+various database modules, such as the <tt class="module">gdbm</tt> or <tt class="module">bsddb</tt>
+modules, that provide ways to write strings to disk and read them
+back.  It's straightforward to combine the <tt class="module">pickle</tt> module and
+a database module to store and retrieve objects, and in fact the
+<tt class="module">shelve</tt> module, included in Python's standard library, does
+this.
+
+<P>
+The downside is that the programmer has to explicitly manage objects,
+reading an object when it's needed and writing it out to disk when the
+object is no longer required.  The ZODB manages objects for you,
+keeping them in a cache and writing them out if they haven't been 
+accessed in a while.  
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node2.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node2.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node4.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node2.html">1 Introduction</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node2.html">1 Introduction</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node4.html">1.2 OODBs vs. Relational</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node30.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>3.6 Sample Application: chatter.py</title>
+<META NAME="description" CONTENT="3.6 Sample Application: chatter.py">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="previous" HREF="node29.html">
+<LINK REL="up" href="zeo.html">
+<LINK REL="next" HREF="node31.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node29.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A href="zeo.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node31.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node29.html">3.5 ZEO Programming Notes</A>
+<b class="navlabel">Up:</b> <a class="sectref" href="zeo.html">3 ZEO</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node31.html">4 Transactions and Versioning</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000460000000000000000">
+3.6 Sample Application: chatter.py</A>
+</H2>
+
+<P>
+For an example application, we'll build a little chat application.
+What's interesting is that none of the application's code deals with
+network programming at all; instead, an object will hold chat
+messages, and be magically shared between all the clients through ZEO.
+I won't present the complete script here; it's included in my ZODB
+distribution, and you can download it from
+<a class="url" href="http://www.amk.ca/zodb/demos/">http://www.amk.ca/zodb/demos/</a>.  Only the interesting portions of
+the code will be covered here.
+
+<P>
+The basic data structure is the <tt class="class">ChatSession</tt> object,
+which provides an <tt class="method">add_message()</tt> method that adds a
+message, and a <tt class="method">new_messages()</tt> method that returns a list
+of new messages that have accumulated since the last call to
+<tt class="method">new_messages()</tt>.  Internally, <tt class="class">ChatSession</tt>
+maintains a B-tree that uses the time as the key, and stores the
+message as the corresponding value.
+
+<P>
+The constructor for <tt class="class">ChatSession</tt> is pretty simple; it simply
+creates an attribute containing a B-tree:
+
+<P>
+<dl><dd><pre class="verbatim">
+class ChatSession(Persistent):
+    def __init__(self, name):
+        self.name = name
+        # Internal attribute: _messages holds all the chat messages.        
+        self._messages = BTree.BTree()
+</pre></dl>
+
+<P>
+<tt class="method">add_message()</tt> has to add a message to the
+<code>_messages</code> B-tree.  A complication is that it's possible
+that some other client is trying to add a message at the same time;
+when this happens, the client that commits first wins, and the second
+client will get a <tt class="exception">ConflictError</tt> exception when it tries to
+commit.  For this application, <tt class="exception">ConflictError</tt> isn't serious
+but simply means that the operation has to be retried; other
+applications might treat it as a fatal error.  The code uses
+<code>try...except...else</code> inside a <code>while</code> loop,
+breaking out of the loop when the commit works without raising an
+exception.
+
+<P>
+<dl><dd><pre class="verbatim">
+    def add_message(self, message):
+        """Add a message to the channel.
+        message -- text of the message to be added
+        """
+
+        while 1:
+            try:
+                now = time.time()
+                self._messages[now] = message
+                get_transaction().commit()
+            except ConflictError:
+                # Conflict occurred; this process should pause and
+                # wait for a little bit, then try again.
+                time.sleep(.2)
+                pass
+            else:
+                # No ConflictError exception raised, so break
+                # out of the enclosing while loop.
+                break
+        # end while
+</pre></dl>
+
+<P>
+<tt class="method">new_messages()</tt> introduces the use of <i>volatile</i>
+attributes.  Attributes of a persistent object that begin with
+<code>_v_</code> are considered volatile and are never stored in the
+database.  <tt class="method">new_messages()</tt> needs to store the last time
+the method was called, but if the time was stored as a regular
+attribute, its value would be committed to the database and shared
+with all the other clients.  <tt class="method">new_messages()</tt> would then
+return the new messages accumulated since any other client called
+<tt class="method">new_messages()</tt>, which isn't what we want.
+
+<P>
+<dl><dd><pre class="verbatim">
+    def new_messages(self):
+        "Return new messages."
+
+        # self._v_last_time is the time of the most recent message
+        # returned to the user of this class. 
+        if not hasattr(self, '_v_last_time'):
+            self._v_last_time = 0
+
+        new = []
+        T = self._v_last_time
+
+        for T2, message in self._messages.items():
+            if T2 &gt; T:
+                new.append(message)
+                self._v_last_time = T2
+
+        return new
+</pre></dl>
+
+<P>
+This application is interesting because it uses ZEO to easily share a
+data structure; ZEO and ZODB are being used for their networking
+ability, not primarily for their data storage ability.  I can foresee
+many interesting applications using ZEO in this way:
+
+<P>
+
+<UL>
+<LI>With a Tkinter front-end, and a cleverer, more scalable data
+  structure, you could build a shared whiteboard using the same
+  technique.
+
+<P>
+</LI>
+<LI>A shared chessboard object would make writing a networked chess
+  game easy.  
+
+<P>
+</LI>
+<LI>You could create a Python class containing a CD's title and
+  track information.  To make a CD database, a read-only ZEO server
+  could be opened to the world, or an HTTP or XML-RPC interface could
+  be written on top of the ZODB.
+
+<P>
+</LI>
+<LI>A program like Quicken could use a ZODB on the local disk to
+  store its data.  This avoids the need to write and maintain
+  specialized I/O code that reads in your objects and writes them out;
+  instead you can concentrate on the problem domain, writing objects
+  that represent cheques, stock portfolios, or whatever.
+
+<P>
+</LI>
+</UL>
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node29.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A href="zeo.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node31.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node29.html">3.5 ZEO Programming Notes</A>
+<b class="navlabel">Up:</b> <a class="sectref" href="zeo.html">3 ZEO</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node31.html">4 Transactions and Versioning</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node31.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>4 Transactions and Versioning</title>
+<META NAME="description" CONTENT="4 Transactions and Versioning">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node36.html">
+<LINK REL="previous" href="zeo.html">
+<LINK REL="up" HREF="zodb.html">
+<LINK REL="next" HREF="node32.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node30.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="zodb.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node32.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node30.html">3.6 Sample Application: chatter.py</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="zodb.html">ZODB/ZEO Programming Guide</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node32.html">4.1 Subtransactions</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H1><A NAME="SECTION000500000000000000000">
+4 Transactions and Versioning</A>
+</H1>
+
+<P>
+
+<p><hr>
+<!--Table of Child-Links-->
+<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a>
+
+<UL>
+<LI><A href="node32.html">4.1 Subtransactions</a>
+<LI><A href="node33.html">4.2 Undoing Changes</a>
+<LI><A href="node34.html">4.3 Versions</a>
+<LI><A href="node35.html">4.4 Multithreaded ZODB Programs</a>
+</ul>
+<!--End of Table of Child-Links-->
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node30.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="zodb.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node32.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node30.html">3.6 Sample Application: chatter.py</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="zodb.html">ZODB/ZEO Programming Guide</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node32.html">4.1 Subtransactions</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node32.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>4.1 Subtransactions</title>
+<META NAME="description" CONTENT="4.1 Subtransactions">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node33.html">
+<LINK REL="previous" HREF="node31.html">
+<LINK REL="up" HREF="node31.html">
+<LINK REL="next" HREF="node33.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node31.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node31.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node33.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node31.html">4 Transactions and Versioning</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node31.html">4 Transactions and Versioning</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node33.html">4.2 Undoing Changes</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000510000000000000000">
+4.1 Subtransactions</A>
+</H2>
+
+<P>
+Subtransactions can be created within a transaction.  Each
+subtransaction can be individually committed and aborted, but the
+changes within a subtransaction are not truly committed until the
+containing transaction is committed.
+
+<P>
+The primary purpose of subtransactions is to decrease the memory usage
+of transactions that touch a very large number of objects.  Consider a
+transaction during which 200,000 objects are modified.  All the
+objects that are modified in a single transaction have to remain in
+memory until the transaction is committed, because the ZODB can't
+discard them from the object cache.  This can potentially make the
+memory usage quite large.  With subtransactions, a commit can be be
+performed at intervals, say, every 10,000 objects.  Those 10,000
+objects are then written to permanent storage and can be purged from
+the cache to free more space.
+
+<P>
+To commit a subtransaction instead of a full transaction, 
+pass a true value to the <tt class="method">commit()</tt>
+or <tt class="method">abort()</tt> method of the <tt class="class">Transaction</tt> object.
+
+<P>
+<dl><dd><pre class="verbatim">
+# Commit a subtransaction
+get_transaction().commit(1)	
+
+# Abort a subtransaction
+get_transaction().abort(1)
+</pre></dl>
+
+<P>
+A new subtransaction is automatically started on committing or
+aborting the previous subtransaction.
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node31.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node31.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node33.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node31.html">4 Transactions and Versioning</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node31.html">4 Transactions and Versioning</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node33.html">4.2 Undoing Changes</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node33.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>4.2 Undoing Changes</title>
+<META NAME="description" CONTENT="4.2 Undoing Changes">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node34.html">
+<LINK REL="previous" HREF="node32.html">
+<LINK REL="up" HREF="node31.html">
+<LINK REL="next" HREF="node34.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node32.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node31.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node34.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node32.html">4.1 Subtransactions</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node31.html">4 Transactions and Versioning</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node34.html">4.3 Versions</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000520000000000000000">
+4.2 Undoing Changes</A>
+</H2>
+
+<P>
+Some types of <tt class="class">Storage</tt> support undoing a transaction even after
+it's been committed.  You can tell if this is the case by calling the
+<tt class="method">supportsUndo()</tt> method of the <tt class="class">DB</tt> instance, which
+returns true if the underlying storage supports undo.  Alternatively
+you can call the <tt class="method">supportsUndo()</tt> method on the underlying
+storage instance.
+
+<P>
+If a database supports undo, then the <tt class="method">undoLog(<var>start</var>,
+<var>end</var><big>[</big>, func<big>]</big>)</tt> method on the <tt class="class">DB</tt> instance returns
+the log of past transactions, returning transactions between the times
+<var>start</var> and <var>end</var>, measured in seconds from the epoch.   
+If present, <var>func</var> is a function that acts as a filter on the
+transactions to be returned; it's passed a dictionary representing
+each transaction, and only transactions for which <var>func</var> returns
+true will be included in the list of transactions returned to the
+caller of <tt class="method">undoLog()</tt>.  The dictionary contains keys for
+various properties of the transaction.  The most important keys are
+"<tt class="samp">id</tt>", for the transaction ID, and "<tt class="samp">time</tt>", for the time at
+which the transaction was committed.  
+
+<P>
+<dl><dd><pre class="verbatim">
+&gt;&gt;&gt; print storage.undoLog(0, sys.maxint)
+[{'description': '',
+  'id': 'AzpGEGqU/0QAAAAAAAAGMA',
+  'time': 981126744.98,
+  'user_name': ''},
+ {'description': '',
+  'id': 'AzpGC/hUOKoAAAAAAAAFDQ',
+  'time': 981126478.202,
+  'user_name': ''}
+  ...
+</pre></dl>
+
+<P>
+To store a description and a user name on a commit, get the current
+transaction and call the <tt class="method">note(<var>text</var>)</tt> method to store a
+description, and the
+<tt class="method">setUser(<var>user_name</var>)</tt> method to store the user name.  
+While <tt class="method">setUser()</tt> overwrites the current user name and replaces
+it with the new value, the <tt class="method">note()</tt> method always adds the text
+to the transaction's description, so it can be called several times to
+log several different changes made in the course of a single
+transaction.
+
+<P>
+<dl><dd><pre class="verbatim">
+get_transaction().setUser('amk')
+get_transaction().note('Change ownership')
+</pre></dl>
+
+<P>
+To undo a transaction, call the <tt class="method">DB.undo(<var>id</var>)</tt> method,
+passing it the ID of the transaction to undo.  If the transaction
+can't be undone, a <tt class="exception">ZODB.POSException.UndoError</tt> exception
+will be raised, with the message ``non-undoable
+transaction''.  Usually this will happen because later transactions
+modified the objects affected by the transaction you're trying to
+undo.
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node32.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node31.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node34.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node32.html">4.1 Subtransactions</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node31.html">4 Transactions and Versioning</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node34.html">4.3 Versions</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node34.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>4.3 Versions</title>
+<META NAME="description" CONTENT="4.3 Versions">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node35.html">
+<LINK REL="previous" HREF="node33.html">
+<LINK REL="up" HREF="node31.html">
+<LINK REL="next" HREF="node35.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node33.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node31.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node35.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node33.html">4.2 Undoing Changes</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node31.html">4 Transactions and Versioning</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node35.html">4.4 Multithreaded ZODB Programs</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000530000000000000000">
+4.3 Versions</A>
+</H2>
+
+<P>
+While many subtransactions can be contained within a single regular
+transaction, it's also possible to contain many regular transactions
+within a long-running transaction, called a version in ZODB
+terminology.  Inside a version, any number of transactions can be
+created and committed or rolled back, but the changes within a version
+are not made visible to other connections to the same ZODB.
+
+<P>
+Not all storages support versions, but you can test for versioning
+ability by calling <tt class="method">supportsVersions()</tt> method of the
+<tt class="class">DB</tt> instance, which returns true if the underlying storage
+supports versioning.
+
+<P>
+A version can be selected when creating the <tt class="class">Connection</tt>
+instance using the <tt class="method">DB.open(<big>[</big><var>version</var><big>]</big>)</tt> method.
+The <var>version</var> argument must be a string that will be used as the
+name of the version.
+
+<P>
+<dl><dd><pre class="verbatim">
+vers_conn = db.open(version='Working version')
+</pre></dl>
+
+<P>
+Transactions can then be committed and aborted using this versioned
+connection.  Other connections that don't specify a version, or
+provide a different version name, will not see changes committed
+within the version named "<tt class="samp">Working&nbsp;version</tt>".  To commit or abort a
+version, which will either make the changes visible to all clients or
+roll them back, call the <tt class="method">DB.commitVersion()</tt> or
+<tt class="method">DB.abortVersion()</tt> methods.
+XXX what are the source and dest arguments for?
+
+<P>
+The ZODB makes no attempt to reconcile changes between different
+versions.  Instead, the first version which modifies an object will
+gain a lock on that object.  Attempting to modify the object from a
+different version or from an unversioned connection will cause a
+<tt class="exception">ZODB.POSException.VersionLockError</tt> to be raised:
+
+<P>
+<dl><dd><pre class="verbatim">
+from ZODB.POSException import VersionLockError
+
+try:
+    get_transaction().commit()
+except VersionLockError, (obj_id, version):
+    print ('Cannot commit; object %s '
+           'locked by version %s' % (obj_id, version))
+</pre></dl>
+
+<P>
+The exception provides the ID of the locked object, and the name of
+the version having a lock on it.
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node33.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node31.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node35.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node33.html">4.2 Undoing Changes</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node31.html">4 Transactions and Versioning</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node35.html">4.4 Multithreaded ZODB Programs</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node35.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>4.4 Multithreaded ZODB Programs</title>
+<META NAME="description" CONTENT="4.4 Multithreaded ZODB Programs">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="previous" HREF="node34.html">
+<LINK REL="up" HREF="node31.html">
+<LINK REL="next" HREF="node36.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node34.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node31.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node36.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node34.html">4.3 Versions</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node31.html">4 Transactions and Versioning</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node36.html">5 Related Modules</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000540000000000000000">
+4.4 Multithreaded ZODB Programs</A>
+</H2>
+
+<P>
+ZODB databases can be accessed from multithreaded Python programs.
+The <tt class="class">Storage</tt> and <tt class="class">DB</tt> instances can be shared among
+several threads, as long as individual <tt class="class">Connection</tt> instances
+are created for each thread.  
+
+<P>
+XXX I can't think of anything else to say about multithreaded ZODB
+programs.  Suggestions?  An example program?
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node34.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node31.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node36.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node34.html">4.3 Versions</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node31.html">4 Transactions and Versioning</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node36.html">5 Related Modules</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node36.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>5 Related Modules</title>
+<META NAME="description" CONTENT="5 Related Modules">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node40.html">
+<LINK REL="previous" HREF="node31.html">
+<LINK REL="up" HREF="zodb.html">
+<LINK REL="next" HREF="node37.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node35.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="zodb.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node37.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node35.html">4.4 Multithreaded ZODB Programs</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="zodb.html">ZODB/ZEO Programming Guide</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node37.html">5.1 ZODB.PersistentMapping</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H1><A NAME="SECTION000600000000000000000">
+5 Related Modules</A>
+</H1>
+
+<P>
+The ZODB package includes a number of related modules that provide
+useful data types such as BTrees or full-text indexes.
+
+<P>
+
+<p><hr>
+<!--Table of Child-Links-->
+<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a>
+
+<UL>
+<LI><A href="node37.html">5.1 <tt class="module">ZODB.PersistentMapping</tt></a>
+<LI><A href="node38.html">5.2 <tt class="module">ZODB.PersistentList</tt></a>
+<LI><A href="node39.html">5.3 B-tree Modules</a>
+</ul>
+<!--End of Table of Child-Links-->
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node35.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="zodb.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node37.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node35.html">4.4 Multithreaded ZODB Programs</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="zodb.html">ZODB/ZEO Programming Guide</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node37.html">5.1 ZODB.PersistentMapping</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node37.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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+<title>5.1 ZODB.PersistentMapping</title>
+<META NAME="description" CONTENT="5.1 ZODB.PersistentMapping">
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+<LINK REL="previous" HREF="node36.html">
+<LINK REL="up" HREF="node36.html">
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+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node36.html"><img src="/python/writing/icons/previous.gif"
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+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node36.html">5 Related Modules</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node36.html">5 Related Modules</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node38.html">5.2 ZODB.PersistentList</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000610000000000000000">
+5.1 <tt class="module">ZODB.PersistentMapping</tt></A>
+</H2>
+
+<P>
+The <tt class="class">PersistentMapping</tt> class is a wrapper for mapping objects
+that will set the dirty bit when the mapping is modified by setting or
+deleting a key.  
+
+<P>
+<dl><dt><b><a name="l2h-1"><tt class="function">PersistentMapping</tt></a></b>(<var>container = {}</var>)
+<dd>
+Create a <tt class="class">PersistentMapping</tt> object that wraps the 
+mapping object <var>container</var>.  If you don't specify a
+value for <var>container</var>, a regular Python dictionary is used.
+</dl>
+
+<P>
+<tt class="class">PersistentMapping</tt> objects support all the same methods as 
+Python dictionaries do.
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node36.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node36.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
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+<td><A HREF="node38.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node36.html">5 Related Modules</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node36.html">5 Related Modules</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node38.html">5.2 ZODB.PersistentList</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node38.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>5.2 ZODB.PersistentList</title>
+<META NAME="description" CONTENT="5.2 ZODB.PersistentList">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node39.html">
+<LINK REL="previous" HREF="node37.html">
+<LINK REL="up" HREF="node36.html">
+<LINK REL="next" HREF="node39.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node37.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node36.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node39.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node37.html">5.1 ZODB.PersistentMapping</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node36.html">5 Related Modules</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node39.html">5.3 B-tree Modules</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000620000000000000000">
+5.2 <tt class="module">ZODB.PersistentList</tt></A>
+</H2>
+
+<P>
+The <tt class="class">PersistentList</tt> class is a wrapper for mutable sequence objects, 
+much as <tt class="class">PersistentMapping</tt> is a wrapper for mappings.  
+
+<P>
+<dl><dt><b><a name="l2h-2"><tt class="function">PersistentList</tt></a></b>(<var>initlist = []</var>)
+<dd>
+Create a <tt class="class">PersistentList</tt> object that wraps the 
+mutable sequence object <var>initlist</var>.  If you don't specify a
+value for <var>initlist</var>, a regular Python list is used.
+</dl>
+
+<P>
+<tt class="class">PersistentList</tt> objects support all the same methods as 
+Python lists do.
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node37.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node36.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
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+<td><A HREF="node39.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node37.html">5.1 ZODB.PersistentMapping</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node36.html">5 Related Modules</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node39.html">5.3 B-tree Modules</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node39.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>5.3 B-tree Modules</title>
+<META NAME="description" CONTENT="5.3 B-tree Modules">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="previous" HREF="node38.html">
+<LINK REL="up" HREF="node36.html">
+<LINK REL="next" HREF="node40.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node38.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node36.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node40.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node38.html">5.2 ZODB.PersistentList</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node36.html">5 Related Modules</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node40.html">A. Resources</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000630000000000000000">
+5.3 B-tree Modules</A>
+</H2>
+
+<P>
+When programming with the ZODB, Python dictionaries aren't always what
+you need.  The most important case is where you want to store a very
+large mapping.  When a Python dictionary is accessed in a ZODB, the
+whole dictionary has to be unpickled and brought into memory.  If
+you're storing something very large, such as a 100,000-entry user
+database, unpickling such a large object will be slow.  B-trees are a
+balanced tree data structure that behave like a mapping but distribute
+keys throughout a number of tree nodes.  Nodes are then only unpickled
+and brought into memory as they're accessed, so the entire tree
+doesn't have to occupy memory (unless you really are touching every
+single key).
+
+<P>
+There are four different BTree modules provided.  One of them, the
+<tt class="module">BTree</tt> module, provides the most general data type; the keys
+and values in the B-tree can be any Python object.  Some specialized B-tree
+modules require that the keys, and perhaps even the values, to be of a
+certain type, and provide faster performance because of this limitation.
+
+<P>
+<DL COMPACT>
+<DT> <tt class="module">IOBTree</tt> </DT>
+<DD>requires the keys to be integers.
+The module name reminds you of this; the <tt class="module">IOBTree</tt> module
+maps Integers to Objects.
+
+<P>
+</DD>
+<DT> <tt class="module">OIBTree</tt> </DT>
+<DD>requires the values to be integers,
+mapping Objects to Integers.
+
+<P>
+</DD>
+<DT> <tt class="module">IIBTree</tt> </DT>
+<DD>is strictest, requiring that both keys and values must be integers.
+
+<P>
+</DD>
+</DL>
+
+<P>
+To use a B-tree, simply import the desired module and call the
+constructor, always named <tt class="function">BTree()</tt>, to get a B-tree
+instance, and then use it like any other mapping:
+
+<P>
+<dl><dd><pre class="verbatim">
+import IIBTree
+iimap = IIBTree.BTree()
+iimap[1972] = 27
+</pre></dl>
+
+<P>
+
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node38.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node36.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
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+<td><A HREF="node40.html"><img src="/python/writing/icons/next.gif"
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+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node38.html">5.2 ZODB.PersistentList</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node36.html">5 Related Modules</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node40.html">A. Resources</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node4.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>1.2 OODBs vs. Relational DBs</title>
+<META NAME="description" CONTENT="1.2 OODBs vs. Relational DBs">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node5.html">
+<LINK REL="previous" HREF="node3.html">
+<LINK REL="up" HREF="node2.html">
+<LINK REL="next" HREF="node5.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node3.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
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+<td><A HREF="node2.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
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+<td><A HREF="node5.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node3.html">1.1 What is the</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node2.html">1 Introduction</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node5.html">1.3 What is ZEO?</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000220000000000000000">
+1.2 OODBs vs. Relational DBs</A>
+</H2>
+
+<P>
+Another way to look at it is that the ZODB is a Python-specific
+object-oriented database (OODB).  Commercial object databases for C++
+or Java often require that you jump through some hoops, such as using
+a special preprocessor or avoiding certain data types.  As we'll see,
+the ZODB has some hoops of its own to jump through, but in comparison
+the naturalness of the ZODB is astonishing.
+
+<P>
+Relational databases (RDBs) are far more common than OODBs.
+Relational databases store information in tables; a table consists of
+any number of rows, each row containing several columns of
+information.  (Rows are more formally called relations, which is where
+the term ``relational database'' originates.)
+
+<P>
+Let's look at a concrete example.  The example comes from my day job
+working for the MEMS Exchange, in a greatly simplified version.  The
+job is to track process runs, which are lists of manufacturing steps
+to be performed in a semiconductor fab.  A run is owned by a
+particular user, and has a name and assigned ID number.  Runs consist
+of a number of operations; an operation is a single step to be
+performed, such as depositing something on a wafer or etching
+something off it.
+
+<P>
+Operations may have parameters, which are additional information
+required to perform an operation.  For example, if you're depositing
+something on a wafer, you need to know two things: 1) what you're
+depositing, and 2) how much should be deposited.  You might deposit
+100 microns of silicon oxide, or 1 micron of copper.
+
+<P>
+Mapping these structures to a relational database is straightforward:
+
+<P>
+<dl><dd><pre class="verbatim">
+CREATE TABLE runs (
+  int      run_id,
+  varchar  owner,
+  varchar  title,
+  int      acct_num,
+  primary key(run_id)
+);
+
+CREATE TABLE operations (
+  int      run_id,
+  int      step_num, 
+  varchar  process_id,
+  PRIMARY KEY(run_id, step_num),
+  FOREIGN KEY(run_id) REFERENCES runs(run_id),
+);
+
+CREATE TABLE parameters (
+  int      run_id,
+  int      step_num, 
+  varchar  param_name, 
+  varchar  param_value,
+  PRIMARY KEY(run_id, step_num, param_name)
+  FOREIGN KEY(run_id, step_num) 
+     REFERENCES operations(run_id, step_num),
+);
+</pre></dl>
+
+<P>
+In Python, you would write three classes named <tt class="class">Run</tt>,
+<tt class="class">Operation</tt>, and <tt class="class">Parameter</tt>.  I won't present code for
+defining these classes, since that code is uninteresting at this
+point. Each class would contain a single method to begin with, an
+<tt class="method">__init__</tt> method that assigns default values, such as 0 or
+<code>None</code>, to each attribute of the class.
+
+<P>
+It's not difficult to write Python code that will create a <tt class="class">Run</tt>
+instance and populate it with the data from the relational tables;
+with a little more effort, you can build a straightforward tool,
+usually called an object-relational mapper, to do this automatically.
+(See
+<a class="url" href="http://www.amk.ca/python/unmaintained/ordb.html">http://www.amk.ca/python/unmaintained/ordb.html</a> for a quick hack
+at a Python object-relational mapper, and
+<a class="url" href="http://www.python.org/workshops/1997-10/proceedings/shprentz.html">http://www.python.org/workshops/1997-10/proceedings/shprentz.html</a>for Joel Shprentz's more successful implementation of the same idea;
+Unlike mine, Shprentz's system has been used for actual work.)
+
+<P>
+However, it is difficult to make an object-relational mapper
+reasonably quick; a simple-minded implementation like mine is quite
+slow because it has to do several queries to access all of an object's
+data.  Higher performance object-relational mappers cache objects to
+improve performance, only performing SQL queries when they actually
+need to.
+
+<P>
+That helps if you want to access run number 123 all of a sudden.  But
+what if you want to find all runs where a step has a parameter named
+'thickness' with a value of 2.0?  In the relational version, you have
+two unappealing choices:
+
+<P>
+
+<OL>
+<LI>Write a specialized SQL query for this case: <code>SELECT run_id
+  FROM operations WHERE param_name = 'thickness' AND param_value = 2.0</code>
+
+<P>
+If such queries are common, you can end up with lots of specialized
+  queries.  When the database tables get rearranged, all these queries
+  will need to be modified.
+
+<P>
+</LI>
+<LI>An object-relational mapper doesn't help much.  Scanning
+  through the runs means that the the mapper will perform the required
+  SQL queries to read run #1, and then a simple Python loop can check
+  whether any of its steps have the parameter you're looking for.
+  Repeat for run #2, 3, and so forth.  This does a vast
+  number of SQL queries, and therefore is incredibly slow.
+
+<P>
+</LI>
+</OL>
+
+<P>
+An object database such as ZODB simply stores internal pointers from
+object to object, so reading in a single object is much faster than
+doing a bunch of SQL queries and assembling the results. Scanning all
+runs, therefore, is still inefficient, but not grossly inefficient.
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node3.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
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+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node3.html">1.1 What is the</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node2.html">1 Introduction</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node5.html">1.3 What is ZEO?</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node40.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>A. Resources</title>
+<META NAME="description" CONTENT="A. Resources">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node41.html">
+<LINK REL="previous" HREF="node36.html">
+<LINK REL="up" HREF="zodb.html">
+<LINK REL="next" HREF="node41.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node39.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="zodb.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node41.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node39.html">5.3 B-tree Modules</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="zodb.html">ZODB/ZEO Programming Guide</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H1><A NAME="SECTION000700000000000000000">
+A. Resources</A>
+</H1>
+
+<P>
+ZODB HOWTO, by Michel Pelletier:
+
+<BR>
+Goes into slightly more detail about the rules for writing applications using the ZODB.
+
+<BR><a class="url" href="http://www.zope.org/Members/michel/HowTos/ZODB-How-To">http://www.zope.org/Members/michel/HowTos/ZODB-How-To</a>
+<P>
+Introduction to the Zope Object Database, by Jim Fulton:
+
+<BR>
+Goes into much greater detail, explaining advanced uses of the ZODB and 
+how it's actually implemented.  A definitive reference, and highly recommended.
+
+<BR><a class="url" href="http://www.python.org/workshops/2000-01/proceedings/papers/fulton/zodb3.html">http://www.python.org/workshops/2000-01/proceedings/papers/fulton/zodb3.html</a>
+<P>
+Download link for ZEO: 
+<BR><a class="url" href="http://www.zope.org/Products/ZEO/">http://www.zope.org/Products/ZEO/</a>
+<P>
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node39.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="zodb.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node41.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node39.html">5.3 B-tree Modules</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="zodb.html">ZODB/ZEO Programming Guide</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node41.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>B. GNU Free Documentation License</title>
+<META NAME="description" CONTENT="B. GNU Free Documentation License">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" href="about.html">
+<LINK REL="previous" HREF="node40.html">
+<LINK REL="up" HREF="zodb.html">
+<LINK REL="next" HREF="node42.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node40.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="zodb.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node42.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node40.html">A. Resources</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="zodb.html">ZODB/ZEO Programming Guide</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node42.html">Preamble</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H1><A NAME="SECTION000800000000000000000">
+B. GNU Free Documentation License</A>
+</H1>
+
+<P>
+Version 1.1, March 2000
+<BR>
+<P>
+Copyright <SPAN CLASS="MATH"><IMG
+ WIDTH="20" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
+ SRC="img1.gif"
+ ALT="$\copyright$"></SPAN> 2000  Free Software Foundation, Inc.
+<BR>
+59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+<BR>
+Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
+<P>
+
+<p><hr>
+<!--Table of Child-Links-->
+<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a>
+
+<UL>
+<LI><A href="node42.html">Preamble</a>
+<LI><A href="node43.html">B..1 Applicability and Definitions</a>
+<LI><A href="node44.html">B..2 Verbatim Copying</a>
+<LI><A href="node45.html">B..3 Copying in Quantity</a>
+<LI><A href="node46.html">B..4 Modifications</a>
+<LI><A href="node47.html">B..5 Combining Documents</a>
+<LI><A href="node48.html">B..6 Collections of Documents</a>
+<LI><A href="node49.html">B..7 Aggregation With Independent Works</a>
+<LI><A href="node50.html">B..8 Translation</a>
+<LI><A href="node51.html">B..9 Termination</a>
+<LI><A href="node52.html">B..10 Future Revisions of This Licence</a>
+<LI><A href="node53.html">ADDENDUM: How to use this License for your documents</a>
+</ul>
+<!--End of Table of Child-Links-->
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node40.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="zodb.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node42.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node40.html">A. Resources</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="zodb.html">ZODB/ZEO Programming Guide</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node42.html">Preamble</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node42.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>Preamble</title>
+<META NAME="description" CONTENT="Preamble">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node43.html">
+<LINK REL="previous" HREF="node41.html">
+<LINK REL="up" HREF="node41.html">
+<LINK REL="next" HREF="node43.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node41.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node41.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node43.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node43.html">B..1 Applicability and Definitions</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000810000000000000000">
+Preamble</A>
+</H2>
+
+<P>
+The purpose of this License is to make a manual, textbook, or other
+written document ``free'' in the sense of freedom: to assure everyone
+the effective freedom to copy and redistribute it, with or without
+modifying it, either commercially or noncommercially.  Secondarily,
+this License preserves for the author and publisher a way to get
+credit for their work, while not being considered responsible for
+modifications made by others.
+
+<P>
+This License is a kind of ``copyleft'', which means that derivative
+works of the document must themselves be free in the same sense.  It
+complements the GNU General Public License, which is a copyleft
+license designed for free software.
+
+<P>
+We have designed this License in order to use it for manuals for free
+software, because free software needs free documentation: a free
+program should come with manuals providing the same freedoms that the
+software does.  But this License is not limited to software manuals;
+it can be used for any textual work, regardless of subject matter or
+whether it is published as a printed book.  We recommend this License
+principally for works whose purpose is instruction or reference.
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node41.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node41.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node43.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node43.html">B..1 Applicability and Definitions</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node43.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>B..1 Applicability and Definitions</title>
+<META NAME="description" CONTENT="B..1 Applicability and Definitions">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node44.html">
+<LINK REL="previous" HREF="node42.html">
+<LINK REL="up" HREF="node41.html">
+<LINK REL="next" HREF="node44.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node42.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node41.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node44.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node42.html">Preamble</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node44.html">B..2 Verbatim Copying</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000820000000000000000">
+B..1 Applicability and Definitions</A>
+</H2>
+
+<P>
+This License applies to any manual or other work that contains a
+notice placed by the copyright holder saying it can be distributed
+under the terms of this License.  The ``Document'', below, refers to any
+such manual or work.  Any member of the public is a licensee, and is
+addressed as ``you''.
+
+<P>
+A ``Modified Version'' of the Document means any work containing the
+Document or a portion of it, either copied verbatim, or with
+modifications and/or translated into another language.
+
+<P>
+A ``Secondary Section'' is a named appendix or a front-matter section of
+the Document that deals exclusively with the relationship of the
+publishers or authors of the Document to the Document's overall subject
+(or to related matters) and contains nothing that could fall directly
+within that overall subject.  (For example, if the Document is in part a
+textbook of mathematics, a Secondary Section may not explain any
+mathematics.)  The relationship could be a matter of historical
+connection with the subject or with related matters, or of legal,
+commercial, philosophical, ethical or political position regarding
+them.
+
+<P>
+The ``Invariant Sections'' are certain Secondary Sections whose titles
+are designated, as being those of Invariant Sections, in the notice
+that says that the Document is released under this License.
+
+<P>
+The ``Cover Texts'' are certain short passages of text that are listed,
+as Front-Cover Texts or Back-Cover Texts, in the notice that says that
+the Document is released under this License.
+
+<P>
+A ``Transparent'' copy of the Document means a machine-readable copy,
+represented in a format whose specification is available to the
+general public, whose contents can be viewed and edited directly and
+straightforwardly with generic text editors or (for images composed of
+pixels) generic paint programs or (for drawings) some widely available
+drawing editor, and that is suitable for input to text formatters or
+for automatic translation to a variety of formats suitable for input
+to text formatters.  A copy made in an otherwise Transparent file
+format whose markup has been designed to thwart or discourage
+subsequent modification by readers is not Transparent.  A copy that is
+not ``Transparent'' is called ``Opaque''.
+
+<P>
+Examples of suitable formats for Transparent copies include plain
+ASCII without markup, Texinfo input format, <SPAN CLASS="logo,LaTeX">L<SUP><SMALL>A</SMALL></SUP>T<SMALL>E</SMALL>X</SPAN>&nbsp;input format, SGML
+or XML using a publicly available DTD, and standard-conforming simple
+HTML designed for human modification.  Opaque formats include
+PostScript, PDF, proprietary formats that can be read and edited only
+by proprietary word processors, SGML or XML for which the DTD and/or
+processing tools are not generally available, and the
+machine-generated HTML produced by some word processors for output
+purposes only.
+
+<P>
+The ``Title Page'' means, for a printed book, the title page itself,
+plus such following pages as are needed to hold, legibly, the material
+this License requires to appear in the title page.  For works in
+formats which do not have any title page as such, ``Title Page'' means
+the text near the most prominent appearance of the work's title,
+preceding the beginning of the body of the text.
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node42.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node41.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node44.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node42.html">Preamble</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node44.html">B..2 Verbatim Copying</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node44.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>B..2 Verbatim Copying</title>
+<META NAME="description" CONTENT="B..2 Verbatim Copying">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node45.html">
+<LINK REL="previous" HREF="node43.html">
+<LINK REL="up" HREF="node41.html">
+<LINK REL="next" HREF="node45.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node43.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node41.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node45.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node43.html">B..1 Applicability and Definitions</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node45.html">B..3 Copying in Quantity</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000830000000000000000">
+B..2 Verbatim Copying</A>
+</H2>
+
+<P>
+You may copy and distribute the Document in any medium, either
+commercially or noncommercially, provided that this License, the
+copyright notices, and the license notice saying this License applies
+to the Document are reproduced in all copies, and that you add no other
+conditions whatsoever to those of this License.  You may not use
+technical measures to obstruct or control the reading or further
+copying of the copies you make or distribute.  However, you may accept
+compensation in exchange for copies.  If you distribute a large enough
+number of copies you must also follow the conditions in section 3.
+
+<P>
+You may also lend copies, under the same conditions stated above, and
+you may publicly display copies.
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node43.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node41.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node45.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node43.html">B..1 Applicability and Definitions</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node45.html">B..3 Copying in Quantity</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node45.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>B..3 Copying in Quantity</title>
+<META NAME="description" CONTENT="B..3 Copying in Quantity">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node46.html">
+<LINK REL="previous" HREF="node44.html">
+<LINK REL="up" HREF="node41.html">
+<LINK REL="next" HREF="node46.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node44.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node41.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node46.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node44.html">B..2 Verbatim Copying</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node46.html">B..4 Modifications</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000840000000000000000">
+B..3 Copying in Quantity</A>
+</H2>
+
+<P>
+If you publish printed copies of the Document numbering more than 100,
+and the Document's license notice requires Cover Texts, you must enclose
+the copies in covers that carry, clearly and legibly, all these Cover
+Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on
+the back cover.  Both covers must also clearly and legibly identify
+you as the publisher of these copies.  The front cover must present
+the full title with all words of the title equally prominent and
+visible.  You may add other material on the covers in addition.
+Copying with changes limited to the covers, as long as they preserve
+the title of the Document and satisfy these conditions, can be treated
+as verbatim copying in other respects.
+
+<P>
+If the required texts for either cover are too voluminous to fit
+legibly, you should put the first ones listed (as many as fit
+reasonably) on the actual cover, and continue the rest onto adjacent
+pages.
+
+<P>
+If you publish or distribute Opaque copies of the Document numbering
+more than 100, you must either include a machine-readable Transparent
+copy along with each Opaque copy, or state in or with each Opaque copy
+a publicly-accessible computer-network location containing a complete
+Transparent copy of the Document, free of added material, which the
+general network-using public has access to download anonymously at no
+charge using public-standard network protocols.  If you use the latter
+option, you must take reasonably prudent steps, when you begin
+distribution of Opaque copies in quantity, to ensure that this
+Transparent copy will remain thus accessible at the stated location
+until at least one year after the last time you distribute an Opaque
+copy (directly or through your agents or retailers) of that edition to
+the public.
+
+<P>
+It is requested, but not required, that you contact the authors of the
+Document well before redistributing any large number of copies, to give
+them a chance to provide you with an updated version of the Document.
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node44.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node41.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node46.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node44.html">B..2 Verbatim Copying</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node46.html">B..4 Modifications</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node46.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>B..4 Modifications</title>
+<META NAME="description" CONTENT="B..4 Modifications">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node47.html">
+<LINK REL="previous" HREF="node45.html">
+<LINK REL="up" HREF="node41.html">
+<LINK REL="next" HREF="node47.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node45.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node41.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node47.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node45.html">B..3 Copying in Quantity</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node47.html">B..5 Combining Documents</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000850000000000000000">
+B..4 Modifications</A>
+</H2>
+
+<P>
+You may copy and distribute a Modified Version of the Document under
+the conditions of sections 2 and 3 above, provided that you release
+the Modified Version under precisely this License, with the Modified
+Version filling the role of the Document, thus licensing distribution
+and modification of the Modified Version to whoever possesses a copy
+of it.  In addition, you must do these things in the Modified Version:
+
+<P>
+
+<UL>
+<LI>Use in the Title Page (and on the covers, if any) a title distinct
+   from that of the Document, and from those of previous versions
+   (which should, if there were any, be listed in the History section
+   of the Document).  You may use the same title as a previous version
+   if the original publisher of that version gives permission.
+</LI>
+<LI>List on the Title Page, as authors, one or more persons or entities
+   responsible for authorship of the modifications in the Modified
+   Version, together with at least five of the principal authors of the
+   Document (all of its principal authors, if it has less than five).
+</LI>
+<LI>State on the Title page the name of the publisher of the
+   Modified Version, as the publisher.
+</LI>
+<LI>Preserve all the copyright notices of the Document.
+</LI>
+<LI>Add an appropriate copyright notice for your modifications
+   adjacent to the other copyright notices.
+</LI>
+<LI>Include, immediately after the copyright notices, a license notice
+   giving the public permission to use the Modified Version under the
+   terms of this License, in the form shown in the Addendum below.
+</LI>
+<LI>Preserve in that license notice the full lists of Invariant Sections
+   and required Cover Texts given in the Document's license notice.
+</LI>
+<LI>Include an unaltered copy of this License.
+</LI>
+<LI>Preserve the section entitled ``History'', and its title, and add to
+   it an item stating at least the title, year, new authors, and
+   publisher of the Modified Version as given on the Title Page.  If
+   there is no section entitled ``History'' in the Document, create one
+   stating the title, year, authors, and publisher of the Document as
+   given on its Title Page, then add an item describing the Modified
+   Version as stated in the previous sentence.
+</LI>
+<LI>Preserve the network location, if any, given in the Document for
+   public access to a Transparent copy of the Document, and likewise
+   the network locations given in the Document for previous versions
+   it was based on.  These may be placed in the ``History'' section.
+   You may omit a network location for a work that was published at
+   least four years before the Document itself, or if the original
+   publisher of the version it refers to gives permission.
+</LI>
+<LI>In any section entitled ``Acknowledgements'' or ``Dedications'',
+   preserve the section's title, and preserve in the section all the
+   substance and tone of each of the contributor acknowledgements
+   and/or dedications given therein.
+</LI>
+<LI>Preserve all the Invariant Sections of the Document,
+   unaltered in their text and in their titles.  Section numbers
+   or the equivalent are not considered part of the section titles.
+</LI>
+<LI>Delete any section entitled ``Endorsements''.  Such a section
+   may not be included in the Modified Version.
+</LI>
+<LI>Do not retitle any existing section as ``Endorsements''
+   or to conflict in title with any Invariant Section.
+
+<P>
+</LI>
+</UL>
+
+<P>
+If the Modified Version includes new front-matter sections or
+appendices that qualify as Secondary Sections and contain no material
+copied from the Document, you may at your option designate some or all
+of these sections as invariant.  To do this, add their titles to the
+list of Invariant Sections in the Modified Version's license notice.
+These titles must be distinct from any other section titles.
+
+<P>
+You may add a section entitled ``Endorsements'', provided it contains
+nothing but endorsements of your Modified Version by various
+parties - for example, statements of peer review or that the text has
+been approved by an organization as the authoritative definition of a
+standard.
+
+<P>
+You may add a passage of up to five words as a Front-Cover Text, and a
+passage of up to 25 words as a Back-Cover Text, to the end of the list
+of Cover Texts in the Modified Version.  Only one passage of
+Front-Cover Text and one of Back-Cover Text may be added by (or
+through arrangements made by) any one entity.  If the Document already
+includes a cover text for the same cover, previously added by you or
+by arrangement made by the same entity you are acting on behalf of,
+you may not add another; but you may replace the old one, on explicit
+permission from the previous publisher that added the old one.
+
+<P>
+The author(s) and publisher(s) of the Document do not by this License
+give permission to use their names for publicity for or to assert or
+imply endorsement of any Modified Version.
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node45.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node41.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node47.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node45.html">B..3 Copying in Quantity</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node47.html">B..5 Combining Documents</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node47.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>B..5 Combining Documents</title>
+<META NAME="description" CONTENT="B..5 Combining Documents">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node48.html">
+<LINK REL="previous" HREF="node46.html">
+<LINK REL="up" HREF="node41.html">
+<LINK REL="next" HREF="node48.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node46.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node41.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node48.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node46.html">B..4 Modifications</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node48.html">B..6 Collections of Documents</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000860000000000000000">
+B..5 Combining Documents</A>
+</H2>
+
+<P>
+You may combine the Document with other documents released under this
+License, under the terms defined in section 4 above for modified
+versions, provided that you include in the combination all of the
+Invariant Sections of all of the original documents, unmodified, and
+list them all as Invariant Sections of your combined work in its
+license notice.
+
+<P>
+The combined work need only contain one copy of this License, and
+multiple identical Invariant Sections may be replaced with a single
+copy.  If there are multiple Invariant Sections with the same name but
+different contents, make the title of each such section unique by
+adding at the end of it, in parentheses, the name of the original
+author or publisher of that section if known, or else a unique number.
+Make the same adjustment to the section titles in the list of
+Invariant Sections in the license notice of the combined work.
+
+<P>
+In the combination, you must combine any sections entitled ``History''
+in the various original documents, forming one section entitled
+``History''; likewise combine any sections entitled ``Acknowledgements'',
+and any sections entitled ``Dedications''.  You must delete all sections
+entitled ``Endorsements.''
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node46.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node41.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node48.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node46.html">B..4 Modifications</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node48.html">B..6 Collections of Documents</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node48.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>B..6 Collections of Documents</title>
+<META NAME="description" CONTENT="B..6 Collections of Documents">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node49.html">
+<LINK REL="previous" HREF="node47.html">
+<LINK REL="up" HREF="node41.html">
+<LINK REL="next" HREF="node49.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node47.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node41.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node49.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node47.html">B..5 Combining Documents</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node49.html">B..7 Aggregation With Independent</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000870000000000000000">
+B..6 Collections of Documents</A>
+</H2>
+
+<P>
+You may make a collection consisting of the Document and other documents
+released under this License, and replace the individual copies of this
+License in the various documents with a single copy that is included in
+the collection, provided that you follow the rules of this License for
+verbatim copying of each of the documents in all other respects.
+
+<P>
+You may extract a single document from such a collection, and distribute
+it individually under this License, provided you insert a copy of this
+License into the extracted document, and follow this License in all
+other respects regarding verbatim copying of that document.
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node47.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node41.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node49.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node47.html">B..5 Combining Documents</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node49.html">B..7 Aggregation With Independent</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node49.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>B..7 Aggregation With Independent Works</title>
+<META NAME="description" CONTENT="B..7 Aggregation With Independent Works">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node50.html">
+<LINK REL="previous" HREF="node48.html">
+<LINK REL="up" HREF="node41.html">
+<LINK REL="next" HREF="node50.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node48.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node41.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node50.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node48.html">B..6 Collections of Documents</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node50.html">B..8 Translation</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000880000000000000000">
+B..7 Aggregation With Independent Works</A>
+</H2>
+
+<P>
+A compilation of the Document or its derivatives with other separate
+and independent documents or works, in or on a volume of a storage or
+distribution medium, does not as a whole count as a Modified Version
+of the Document, provided no compilation copyright is claimed for the
+compilation.  Such a compilation is called an ``aggregate'', and this
+License does not apply to the other self-contained works thus compiled
+with the Document, on account of their being thus compiled, if they
+are not themselves derivative works of the Document.
+
+<P>
+If the Cover Text requirement of section 3 is applicable to these
+copies of the Document, then if the Document is less than one quarter
+of the entire aggregate, the Document's Cover Texts may be placed on
+covers that surround only the Document within the aggregate.
+Otherwise they must appear on covers around the whole aggregate.
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node48.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node41.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node50.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node48.html">B..6 Collections of Documents</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node50.html">B..8 Translation</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node5.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>1.3 What is ZEO?</title>
+<META NAME="description" CONTENT="1.3 What is ZEO?">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node6.html">
+<LINK REL="previous" HREF="node4.html">
+<LINK REL="up" HREF="node2.html">
+<LINK REL="next" HREF="node6.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node4.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node2.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node6.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node4.html">1.2 OODBs vs. Relational</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node2.html">1 Introduction</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node6.html">1.4 About this guide</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000230000000000000000">
+1.3 What is ZEO?</A>
+</H2>
+
+<P>
+The ZODB comes with a few different classes that implement the
+<tt class="class">Storage</tt> interface.  Such classes handle the job of
+writing out Python objects to a physical storage medium, which can be
+a disk file (the <tt class="class">FileStorage</tt> class), a BerkeleyDB file
+(<tt class="class">BerkeleyStorage</tt>), a relational database
+(<tt class="class">DCOracleStorage</tt>), or some other medium.  ZEO adds
+<tt class="class">ClientStorage</tt>, a new <tt class="class">Storage</tt> that doesn't write to
+physical media but just forwards all requests across a network to a
+server.  The server, which is running an instance of the
+<tt class="class">StorageServer</tt> class, simply acts as a front-end for some
+physical <tt class="class">Storage</tt> class.  It's a fairly simple idea, but as
+we'll see later on in this document, it opens up many possibilities.
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node4.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node2.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node6.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node4.html">1.2 OODBs vs. Relational</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node2.html">1 Introduction</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node6.html">1.4 About this guide</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node50.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>B..8 Translation</title>
+<META NAME="description" CONTENT="B..8 Translation">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node51.html">
+<LINK REL="previous" HREF="node49.html">
+<LINK REL="up" HREF="node41.html">
+<LINK REL="next" HREF="node51.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node49.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node41.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node51.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node49.html">B..7 Aggregation With Independent</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node51.html">B..9 Termination</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000890000000000000000">
+B..8 Translation</A>
+</H2>
+
+<P>
+Translation is considered a kind of modification, so you may
+distribute translations of the Document under the terms of section 4.
+Replacing Invariant Sections with translations requires special
+permission from their copyright holders, but you may include
+translations of some or all Invariant Sections in addition to the
+original versions of these Invariant Sections.  You may include a
+translation of this License provided that you also include the
+original English version of this License.  In case of a disagreement
+between the translation and the original English version of this
+License, the original English version will prevail.
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node49.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node41.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node51.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node49.html">B..7 Aggregation With Independent</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node51.html">B..9 Termination</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node51.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>B..9 Termination</title>
+<META NAME="description" CONTENT="B..9 Termination">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node52.html">
+<LINK REL="previous" HREF="node50.html">
+<LINK REL="up" HREF="node41.html">
+<LINK REL="next" HREF="node52.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node50.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node41.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node52.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node50.html">B..8 Translation</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node52.html">B..10 Future Revisions of</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION0008100000000000000000">
+B..9 Termination</A>
+</H2>
+
+<P>
+You may not copy, modify, sublicense, or distribute the Document except
+as expressly provided for under this License.  Any other attempt to
+copy, modify, sublicense or distribute the Document is void, and will
+automatically terminate your rights under this License.  However,
+parties who have received copies, or rights, from you under this
+License will not have their licenses terminated so long as such
+parties remain in full compliance.
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node50.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node41.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node52.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node50.html">B..8 Translation</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node52.html">B..10 Future Revisions of</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node52.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>B..10 Future Revisions of This Licence</title>
+<META NAME="description" CONTENT="B..10 Future Revisions of This Licence">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node53.html">
+<LINK REL="previous" HREF="node51.html">
+<LINK REL="up" HREF="node41.html">
+<LINK REL="next" HREF="node53.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node51.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node41.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node53.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node51.html">B..9 Termination</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node53.html">ADDENDUM: How to use</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION0008110000000000000000">
+B..10 Future Revisions of This Licence</A>
+</H2>
+
+<P>
+The Free Software Foundation may publish new, revised versions
+of the GNU Free Documentation License from time to time.  Such new
+versions will be similar in spirit to the present version, but may
+differ in detail to address new problems or concerns. See
+<a class="url" href="http://www.gnu.org/copyleft/">http://www.gnu.org/copyleft/</a>.
+
+<P>
+Each version of the License is given a distinguishing version number.
+If the Document specifies that a particular numbered version of this
+License "or any later version" applies to it, you have the option of
+following the terms and conditions either of that specified version or
+of any later version that has been published (not as a draft) by the
+Free Software Foundation.  If the Document does not specify a version
+number of this License, you may choose any version ever published (not
+as a draft) by the Free Software Foundation.
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node51.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node41.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node53.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node51.html">B..9 Termination</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node53.html">ADDENDUM: How to use</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node53.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>ADDENDUM: How to use this License for your documents</title>
+<META NAME="description" CONTENT="ADDENDUM: How to use this License for your documents">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="previous" HREF="node52.html">
+<LINK REL="up" HREF="node41.html">
+<LINK REL="next" href="about.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node52.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node41.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A href="about.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node52.html">B..10 Future Revisions of</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
+<b class="navlabel">Next:</b> <a class="sectref" href="about.html">About this document ...</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION0008120000000000000000">
+ADDENDUM: How to use this License for your documents</A>
+</H2>
+
+<P>
+To use this License in a document you have written, include a copy of
+the License in the document and put the following copyright and
+license notices just after the title page:
+
+<P>
+<P>
+<BLOCKQUOTE>Copyright <SPAN CLASS="MATH"><IMG
+ WIDTH="20" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
+ SRC="img1.gif"
+ ALT="$\copyright$"></SPAN> YEAR  YOUR NAME.
+      Permission is granted to copy, distribute and/or modify this document
+      under the terms of the GNU Free Documentation License, Version 1.1
+      or any later version published by the Free Software Foundation;
+      with the Invariant Sections being LIST THEIR TITLES, with the
+      Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.
+      A copy of the license is included in the section entitled ``GNU
+      Free Documentation License''.
+</BLOCKQUOTE>
+<P>
+
+<P>
+If you have no Invariant Sections, write ``with no Invariant Sections''
+instead of saying which ones are invariant.  If you have no
+Front-Cover Texts, write ``no Front-Cover Texts'' instead of
+``Front-Cover Texts being LIST''; likewise for Back-Cover Texts.
+
+<P>
+If your document contains nontrivial examples of program code, we
+recommend releasing these examples in parallel under your choice of
+free software license, such as the GNU General Public License,
+to permit their use in free software.
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node52.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node41.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A href="about.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node52.html">B..10 Future Revisions of</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
+<b class="navlabel">Next:</b> <a class="sectref" href="about.html">About this document ...</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node6.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>1.4 About this guide</title>
+<META NAME="description" CONTENT="1.4 About this guide">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node7.html">
+<LINK REL="previous" HREF="node5.html">
+<LINK REL="up" HREF="node2.html">
+<LINK REL="next" HREF="node7.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node5.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node2.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node7.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node5.html">1.3 What is ZEO?</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node2.html">1 Introduction</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node7.html">1.5 Acknowledgements</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000240000000000000000">
+1.4 About this guide</A>
+</H2>
+
+<P>
+The primary author of this guide works on a project which uses the
+ZODB and ZEO as its primary storage technology.  We use the ZODB to
+store process runs and operations, a catalog of available processes,
+user information, accounting information, and other data.  Part of the
+goal of writing this document is to make our experience more widely
+available.  A few times we've spent hours or even days trying to
+figure out a problem, and this guide is an attempt to gather up the
+knowledge we've gained so that others don't have to make the same
+mistakes we did while learning.
+
+<P>
+This document will always be a work in progress.  If you wish to
+suggest clarifications or additional topics, please send your comments to
+<span class="email">akuchlin@mems-exchange.org</span>.  
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node5.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node2.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node7.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node5.html">1.3 What is ZEO?</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node2.html">1 Introduction</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node7.html">1.5 Acknowledgements</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node7.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>1.5 Acknowledgements</title>
+<META NAME="description" CONTENT="1.5 Acknowledgements">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="previous" HREF="node6.html">
+<LINK REL="up" HREF="node2.html">
+<LINK REL="next" HREF="node8.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node6.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node2.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node8.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node6.html">1.4 About this guide</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node2.html">1 Introduction</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node8.html">2 ZODB Programming</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000250000000000000000">
+1.5 Acknowledgements</A>
+</H2>
+
+<P>
+I'd like to thank the people who've pointed out inaccuracies and bugs,
+offered suggestions on the text, or proposed new topics that should be
+covered: Jeff Bauer, Willem Broekema, Thomas Guettler,
+Chris McDonough, George Runyan.
+
+<P>
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node6.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node2.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node8.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node6.html">1.4 About this guide</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node2.html">1 Introduction</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node8.html">2 ZODB Programming</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node8.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>2 ZODB Programming</title>
+<META NAME="description" CONTENT="2 ZODB Programming">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" href="zeo.html">
+<LINK REL="previous" HREF="node2.html">
+<LINK REL="up" HREF="zodb.html">
+<LINK REL="next" HREF="node9.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node7.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="zodb.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node9.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node7.html">1.5 Acknowledgements</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="zodb.html">ZODB/ZEO Programming Guide</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node9.html">2.1 Installing ZODB</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H1><A NAME="SECTION000300000000000000000">
+2 ZODB Programming</A>
+</H1>
+
+<P>
+
+<p><hr>
+<!--Table of Child-Links-->
+<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a>
+
+<UL>
+<LI><A href="node9.html">2.1 Installing ZODB</a>
+<UL>
+<LI><A href="node10.html">2.1.1 Requirements</a>
+<LI><A href="node11.html">2.1.2 Installing the Packages</a>
+</ul>
+<LI><A href="node12.html">2.2 How ZODB Works</a>
+<LI><A href="node13.html">2.3 Opening a ZODB</a>
+<LI><A href="node14.html">2.4 Writing a Persistent Class</a>
+<LI><A href="node15.html">2.5 Rules for Writing Persistent Classes</a>
+<UL>
+<LI><A href="node16.html">2.5.1 Modifying Mutable Objects</a>
+<LI><A href="node17.html">2.5.2 Some Special Methods Don't Work</a>
+<LI><A href="node18.html">2.5.3 Fixing <tt class="function">isinstance</tt> and <tt class="function">issubclass</tt></a>
+<LI><A href="node19.html">2.5.4 <tt class="method">__getattr__</tt>, <tt class="method">__delattr__</tt>, and <tt class="method">__setattr__</tt></a>
+</ul>
+<LI><A href="node20.html">2.6 Writing Persistent Classes</a>
+<UL>
+<LI><A href="node21.html">2.6.1 Changing Instance Attributes</a>
+</ul></ul>
+<!--End of Table of Child-Links-->
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node7.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="zodb.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node9.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node7.html">1.5 Acknowledgements</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="zodb.html">ZODB/ZEO Programming Guide</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node9.html">2.1 Installing ZODB</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/node9.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>2.1 Installing ZODB</title>
+<META NAME="description" CONTENT="2.1 Installing ZODB">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node12.html">
+<LINK REL="previous" HREF="node8.html">
+<LINK REL="up" HREF="node8.html">
+<LINK REL="next" HREF="node10.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node8.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node8.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node10.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node8.html">2 ZODB Programming</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node8.html">2 ZODB Programming</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node10.html">2.1.1 Requirements</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H2><A NAME="SECTION000310000000000000000">
+2.1 Installing ZODB</A>
+</H2>
+
+<P>
+The ZODB forms part of Zope, but it's difficult and somewhat painful
+to extract the bits from Zope needed to support just the ZODB.
+Therefore I've assembled a distribution containing only the packages
+required to use the ZODB and ZEO, so you can install it and start
+programming right away.
+
+<P>
+To download the distribution, go to my ZODB page at 
+<a class="url" href="http://www.amk.ca/zodb/">http://www.amk.ca/zodb/</a>.  
+The distribution is still experimental, so don't be surprised if the
+installation process runs into problems.  Please inform me of any
+difficulties you encounter.
+
+<P>
+
+<p><hr>
+<!--Table of Child-Links-->
+<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a>
+
+<UL>
+<LI><A href="node10.html">2.1.1 Requirements</a>
+<LI><A href="node11.html">2.1.2 Installing the Packages</a>
+</ul>
+<!--End of Table of Child-Links-->
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node8.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="node8.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node10.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node8.html">2 ZODB Programming</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="node8.html">2 ZODB Programming</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node10.html">2.1.1 Requirements</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/zeo.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>3 ZEO</title>
+<META NAME="description" CONTENT="3 ZEO">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" HREF="node31.html">
+<LINK REL="previous" HREF="node8.html">
+<LINK REL="up" HREF="zodb.html">
+<LINK REL="next" HREF="node23.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node21.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="zodb.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node23.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node21.html">2.6.1 Changing Instance Attributes</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="zodb.html">ZODB/ZEO Programming Guide</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node23.html">3.1 How ZEO Works</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<H1><A NAME="SECTION000400000000000000000">&nbsp;</A>
+<BR>
+3 ZEO
+</H1>
+
+<P>
+
+<p><hr>
+<!--Table of Child-Links-->
+<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a>
+
+<UL>
+<LI><A href="node23.html">3.1 How ZEO Works</a>
+<LI><A href="node24.html">3.2 Installing ZEO</a>
+<UL>
+<LI><A href="node25.html">3.2.1 Requirements</a>
+<LI><A href="node26.html">3.2.2 Installation</a>
+</ul>
+<LI><A href="node27.html">3.3 Configuring and Running a ZEO Server</a>
+<LI><A href="node28.html">3.4 Testing the ZEO Installation</a>
+<LI><A href="node29.html">3.5 ZEO Programming Notes</a>
+<LI><A href="node30.html">3.6 Sample Application: chatter.py</a>
+</ul>
+<!--End of Table of Child-Links-->
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><A HREF="node21.html"><img src="/python/writing/icons/previous.gif"
+  border="0" height="32"
+  alt="Previous Page" width="32"></A></td>
+<td><A HREF="zodb.html"><img src="/python/writing/icons/up.gif"
+  border="0" height="32"
+  alt="Up One Level" width="32"></A></td>
+<td><A HREF="node23.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Previous:</b> <a class="sectref" HREF="node21.html">2.6.1 Changing Instance Attributes</A>
+<b class="navlabel">Up:</b> <a class="sectref" HREF="zodb.html">ZODB/ZEO Programming Guide</A>
+<b class="navlabel">Next:</b> <a class="sectref" HREF="node23.html">3.1 How ZEO Works</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
+<!--End of Navigation Panel-->
+
+</BODY>
+</HTML>

doc/guide/zodb/zodb.css

+/*
+ * The first part of this is the standard CSS generated by LaTeX2HTML,
+ * with the "empty" declarations removed.
+ */
+
+/* Century Schoolbook font is very similar to Computer Modern Math: cmmi */
+.math                   { font-family: "Century Schoolbook", serif; }
+.math i                 { font-family: "Century Schoolbook", serif;
+                          font-weight: bold }
+.boldmath               { font-family: "Century Schoolbook", serif;
+                          font-weight: bold }
+
+/*
+ * Implement both fixed-size and relative sizes.
+ *
+ * I think these can be safely removed, as it doesn't appear that
+ * LaTeX2HTML ever generates these, even though these are carried
+ * over from the LaTeX2HTML stylesheet.
+ */
+small.xtiny             { font-size : xx-small; }
+small.tiny              { font-size : x-small; }
+small.scriptsize        { font-size : smaller; }
+small.footnotesize      { font-size : small; }
+big.xlarge              { font-size : large; }
+big.xxlarge             { font-size : x-large; }
+big.huge                { font-size : larger; }
+big.xhuge               { font-size : xx-large; }
+
+/*
+ * Document-specific styles come next;
+ * these are added for the Python documentation.
+ *
+ * Note that the size specifications for the H* elements are because
+ * Netscape on Solaris otherwise doesn't get it right; they all end up
+ * the normal text size.
+ */
+
+body                    { color: #000000;
+                          background-color: #ffffff; }
+
+a:active                { color: #ff0000; }
+a:visited               { color: #551a8b; }
+a:link                  { color: #0000bb; }
+
+h1, h2, h3, h4, h5, h6  { font-family: avantgarde, sans-serif;
+                          font-weight: bold; }
+h1                      { font-size: 180%; }
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+code, tt                { font-family: lucida typewriter, lucidatypewriter,
+                                       monospace; }
+var                     { font-family: times, serif;
+                          font-style: italic;
+                          font-weight: normal; }
+
+.typelabel              { font-family: lucida, sans-serif; }
+
+.navigation td          { background-color: #99ccff;
+                          font-weight: bold;
+                          font-family: avantgarde, sans-serif;
+                          font-size: 110%; }
+
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+
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+
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+                          font-family: lucida typewriter, lucidatypewriter,
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+
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+                          font-family: avantgarde, sans-serif; }
+
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+.refcount-info .value   { font-weight: bold;
+                          color: #006600; }
+
+/*
+ * Some decoration for the "See also:" blocks, in part inspired by some of
+ * the styling on Lars Marius Garshol's XSA pages.
+ * (The blue in the navigation bars is #99CCFF.)
+ */
+.seealso                { background-color: #fffaf0;
+                          border: thin solid black;
+                          padding: 4pt; }
+
+.seealso .heading       { font-size: 110%; }
+
+/*
+ * Class 'availability' is used for module availability statements at
+ * the top of modules.
+ */
+.availability .platform { font-weight: bold; }

doc/guide/zodb/zodb.html

+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<html>
+<head>
+<title>ZODB/ZEO Programming Guide</title>
+<META NAME="description" CONTENT="ZODB/ZEO Programming Guide">
+<META NAME="keywords" CONTENT="zodb">
+<META NAME="resource-type" CONTENT="document">
+<META NAME="distribution" CONTENT="global">
+<meta http-equiv="Content-Type" content="text/html; charset=">
+<link rel="STYLESHEET" href="zodb.css">
+<link rel="first" href="zodb.html">
+<link rel="contents" href="contents.html" title="Contents">
+
+<LINK REL="next" href="contents.html">
+</head>
+<body>
+<DIV CLASS="navigation">
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><A href="contents.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Next:</b> <a class="sectref" href="contents.html">Contents</A>
+<br><hr>
+</DIV>
+<!--End of Navigation Panel-->
+
+<div class="titlepage">
+<center>
+<h1>ZODB/ZEO Programming Guide</h1>
+<p><b><font size="+2">A.M. Kuchling</font></b></p>
+<p>akuchlin@mems-exchange.org</p>
+<p><strong>Release 0.03</strong><br>
+<strong>February 8, 2002</strong></p>
+<p>
+</center>
+</div>
+
+<p><hr>
+<!--Table of Child-Links-->
+<A NAME="CHILD_LINKS"></a>
+
+<UL>
+<LI><A href="contents.html">Contents</a>
+<LI><A href="node2.html">1 Introduction</a>
+<UL>
+<LI><A href="node3.html">1.1 What is the ZODB?</a>
+<LI><A href="node4.html">1.2 OODBs vs. Relational DBs</a>
+<LI><A href="node5.html">1.3 What is ZEO?</a>
+<LI><A href="node6.html">1.4 About this guide</a>
+<LI><A href="node7.html">1.5 Acknowledgements</a>
+</ul>
+<LI><A href="node8.html">2 ZODB Programming</a>
+<UL>
+<LI><A href="node9.html">2.1 Installing ZODB</a>
+<UL>
+<LI><A href="node10.html">2.1.1 Requirements</a>
+<LI><A href="node11.html">2.1.2 Installing the Packages</a>
+</ul>
+<LI><A href="node12.html">2.2 How ZODB Works</a>
+<LI><A href="node13.html">2.3 Opening a ZODB</a>
+<LI><A href="node14.html">2.4 Writing a Persistent Class</a>
+<LI><A href="node15.html">2.5 Rules for Writing Persistent Classes</a>
+<UL>
+<LI><A href="node16.html">2.5.1 Modifying Mutable Objects</a>
+<LI><A href="node17.html">2.5.2 Some Special Methods Don't Work</a>
+<LI><A href="node18.html">2.5.3 Fixing <tt class="function">isinstance</tt> and <tt class="function">issubclass</tt></a>
+<LI><A href="node19.html">2.5.4 <tt class="method">__getattr__</tt>, <tt class="method">__delattr__</tt>, and <tt class="method">__setattr__</tt></a>
+</ul>
+<LI><A href="node20.html">2.6 Writing Persistent Classes</a>
+<UL>
+<LI><A href="node21.html">2.6.1 Changing Instance Attributes</a>
+</ul>
+</ul>
+<LI><A href="zeo.html">3 ZEO</a>
+<UL>
+<LI><A href="node23.html">3.1 How ZEO Works</a>
+<LI><A href="node24.html">3.2 Installing ZEO</a>
+<UL>
+<LI><A href="node25.html">3.2.1 Requirements</a>
+<LI><A href="node26.html">3.2.2 Installation</a>
+</ul>
+<LI><A href="node27.html">3.3 Configuring and Running a ZEO Server</a>
+<LI><A href="node28.html">3.4 Testing the ZEO Installation</a>
+<LI><A href="node29.html">3.5 ZEO Programming Notes</a>
+<LI><A href="node30.html">3.6 Sample Application: chatter.py</a>
+</ul>
+<LI><A href="node31.html">4 Transactions and Versioning</a>
+<UL>
+<LI><A href="node32.html">4.1 Subtransactions</a>
+<LI><A href="node33.html">4.2 Undoing Changes</a>
+<LI><A href="node34.html">4.3 Versions</a>
+<LI><A href="node35.html">4.4 Multithreaded ZODB Programs</a>
+</ul>
+<LI><A href="node36.html">5 Related Modules</a>
+<UL>
+<LI><A href="node37.html">5.1 <tt class="module">ZODB.PersistentMapping</tt></a>
+<LI><A href="node38.html">5.2 <tt class="module">ZODB.PersistentList</tt></a>
+<LI><A href="node39.html">5.3 B-tree Modules</a>
+</ul>
+<LI><A href="node40.html">A. Resources</a>
+<LI><A href="node41.html">B. GNU Free Documentation License</a>
+<UL>
+<LI><A href="node42.html">Preamble</a>
+<LI><A href="node43.html">B..1 Applicability and Definitions</a>
+<LI><A href="node44.html">B..2 Verbatim Copying</a>
+<LI><A href="node45.html">B..3 Copying in Quantity</a>
+<LI><A href="node46.html">B..4 Modifications</a>
+<LI><A href="node47.html">B..5 Combining Documents</a>
+<LI><A href="node48.html">B..6 Collections of Documents</a>
+<LI><A href="node49.html">B..7 Aggregation With Independent Works</a>
+<LI><A href="node50.html">B..8 Translation</a>
+<LI><A href="node51.html">B..9 Termination</a>
+<LI><A href="node52.html">B..10 Future Revisions of This Licence</a>
+<LI><A href="node53.html">ADDENDUM: How to use this License for your documents</a>
+</ul>
+<LI><A href="about.html">About this document ...</a>
+</ul>
+<!--End of Table of Child-Links-->
+
+<DIV CLASS="navigation">
+<p><hr>
+<table align="center" width="100%" cellpadding="0" cellspacing="2">
+<tr>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><A href="contents.html"><img src="/python/writing/icons/next.gif"
+  border="0" height="32"
+  alt="Next Page" width="32"></A></td>
+<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
+<td><A href="contents.html"><img src="/python/writing/icons/contents.gif"
+  border="0" height="32"
+  alt="Contents" width="32"></A></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+<td><img src="/python/writing/icons/blank.gif"
+  border="0" height="32"
+  alt="" width="32"></td>
+</tr></table>
+<b class="navlabel">Next:</b> <a class="sectref" href="contents.html">Contents</A>
+<hr>
+<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
+</DIV>
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+
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+</HTML>