Commit 880dc94e authored by Tim Peters's avatar Tim Peters

Added minimal IFBTree docs.

parent 5ce266e4
......@@ -29,6 +29,16 @@ DB
raised. In ZODB 3.6, these optional arguments will be removed.
BTrees
------
- A new family of BTree types, in the ``IFBTree`` module, map
signed integers (32 bits) to C floats (also 32 bits). The
intended use is to help construct search indices, where, e.g.,
integer word or document identifiers map to scores of some
kind. This is easier than trying to work with scaled integer
score in an ``IIBTree``, and Zope3 has moved to ``IFBTrees``
for these purposes in its search code.
Tools
-----
......
......@@ -59,11 +59,11 @@ touching every single key).
The BTrees package provides a large collection of related data
structures. There are variants of the data structures specialized to
integers, which are faster and use less memory. There
are four modules that handle the different variants. The first two
are five modules that handle the different variants. The first two
letters of the module name specify the types of the keys and values in
mappings -- O for any object and I for integer. For example, the
\module{BTrees.IOBTree} module provides a mapping with integer
keys and arbitrary objects as values.
mappings -- O for any object, I for 32-bit signed integer, and F for
32-bit C float. For example, the \module{BTrees.IOBTree} module provides
a mapping with integer keys and arbitrary objects as values.
The four data structures provide by each module are a BTree, a Bucket,
a TreeSet, and a Set. The BTree and Bucket types are mappings and
......@@ -85,10 +85,10 @@ is built out of multiple objects, which ZODB can load individually
as needed.
The four modules are named \module{OOBTree}, \module{IOBTree},
\module{OIBTree}, and \module{IIBTree}. The two letter prefixes are
repeated in the data types names. The \module{BTrees.OOBTree} module
defines the following types: \class{OOBTree}, \class{OOBucket},
\class{OOSet}, and \class{OOTreeSet}. Similarly, the other three modules
\module{OIBTree}, \module{IIBTree}, and \module{IFBTree}. The two letter
prefixes are repeated in the data types names. The \module{BTrees.OOBTree}
module defines the following types: \class{OOBTree}, \class{OOBucket},
\class{OOSet}, and \class{OOTreeSet}. Similarly, the other four modules
each define their own variants of those four types.
The \function{keys()}, \function{values()}, and \function{items()}
......@@ -179,8 +179,8 @@ BTrees -- \function{difference()}, \function{union()}, and
\function{intersection()}. The \function{difference()} function returns
a Bucket, while the other two methods return a Set.
If the keys are integers, then the module also defines
\function{multiunion()}. If the values are integers, then the module
also defines \function{weightedIntersection()} and
\function{multiunion()}. If the values are integers or floats, then the
module also defines \function{weightedIntersection()} and
\function{weightedUnion()}. The function doc strings describe each
function briefly.
......
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