# Auto-generated file -- DO NOT EDIT!!!!!

=head1 NAME

KinoSearch::Index::Similarity - Judge how well a document matches a query.


The KinoSearch code base has been assimilated by the Apache L<Lucy> project.
The "KinoSearch" namespace has been deprecated, but development continues
under our new name at our new home: L<http://lucy.apache.org/>


    package MySimilarity;

    sub length_norm { return 1.0 }    # disable length normalization

    package MyFullTextType;
    use base qw( KinoSearch::Plan::FullTextType );

    sub make_similarity { MySimilarity->new }


After determining whether a document matches a given query, a score must be
calculated which indicates how I<well> the document matches the query.  The
Similarity class is used to judge how "similar" the query and the document
are to each other; the closer the resemblance, they higher the document

The default implementation uses Lucene's modified cosine similarity
measure.  Subclasses might tweak the existing algorithms, or might be used
in conjunction with custom Query subclasses to implement arbitrary scoring

Most of the methods operate on single fields, but some are used to combine
scores from multiple fields.


=head2 new()

    my $sim = KinoSearch::Index::Similarity->new;

Constructor. Takes no arguments.

=head1 METHODS

=head2 length_norm(num_tokens)

Dampen the scores of long documents.

After a field is broken up into terms at index-time, each term must be
assigned a weight.  One of the factors in calculating this weight is
the number of tokens that the original field was broken into.

Typically, we assume that the more tokens in a field, the less
important any one of them is -- so that, e.g. 5 mentions of "Kafka" in
a short article are given more heft than 5 mentions of "Kafka" in an
entire book.  The default implementation of length_norm expresses this
using an inverted square root.  

However, the inverted square root has a tendency to reward very short
fields highly, which isn't always appropriate for fields you expect to
have a lot of tokens on average.


KinoSearch::Index::Similarity isa L<KinoSearch::Object::Obj>.


Copyright 2005-2011 Marvin Humphrey

This program is free software; you can redistribute it and/or modify it under
the same terms as Perl itself.