NAME
   XAO::Indexer -- Full text data indexing for XAO::FS

SYNOPSIS
    my $keywords=$cgi->param('keywords');
    my $cn_index=$odb->fetch('/Indexes/customer_names');
    my $sr=$cn_index->search_by_string('name',$keywords);

DESCRIPTION
   XAO Indexer allows to build an optimised external index to collections
   of data stored in a XAO::FS database and then perform keyword based
   searches.

   It is being used with great success on collection of millions of records
   on some sites, probably most notably on <http://ISBNdb.com/> where it
   powers all the searches.

PROBLEM & SOLUTION
   Searches are limited to just keywords, but allow to find many keywords
   in a specific sequence or just many keywords that belong to a specific
   collection, but could be in different properties of different objects.

   To perform the same kind of search on just two properties of an object
   with two possible keywords a join similar to the following is required:

    ( (property1 match keyword1) and (property1 match keyword2) ) or
    ( (property1 match keyword1) and (property2 match keyword2) ) or
    ( (property2 match keyword1) and (property2 match keyword2) ) or
    ( (property2 match keyword1) and (property1 match keyword2) )

   With bigger number of keywords and properties the expression becomes too
   big to be efficiently handled by SQL server and in some cases probably
   to be even parsed normally by an SQL server.

   In addition, such keyword searches are not optimised in SQL databases
   usually and frequently involve full table scans.

   XAO Indexer solves this problem by pre-building a specially formatted
   index table that has results for specific keywords. As an additional
   benefit it allows to get results pre-sorted using some (possibly
   computed) criteria without any performance impact.

   It needs to be mentioned though, that XAO Indexer is not integrated with
   the collection it builds index for in any way. It has to be maintained
   and updated manually and can return IDs of objects that no longer exist
   in the database.

   The process of re-building indexes can take significant time depending
   on the content of source collection. In our tests it takes approximately
   5 minutes to build an index based on 60,000 records 5..50 fields per
   record spread over 3 or more related objects (products, categories and
   specifications).

 STRUCTURE
   XAO::Indexer is a stub module that only holds common documentation that
   you are reading now. Real functionality is provided by:

   XAO::DO::Data::Index
       This is a XAO FS Hash object that gets stored into some container in
       your database, usually /Indexes. It provides wrapper methods to all
       indexing functionality, see XAO::DO::Data::Index for details.

       Most of the time you will interact with this object in your code.
       Something like:

        my $keywords=$cgi->param('keywords');
        my $cn_index=$odb->fetch('/Indexes/customer_names');
        my $sr=$cn_index->search('name',$keywords);

   XAO::DO::Indexer::Base
       This is the core of XAO Indexer -- a base class for derived data
       collection specific indexers. Usually it is enough to override just
       a couple of its methods -- analyze_object(), get_collection() and
       get_orderings(). See XAO::DO::Indexer::Base for details.

   xao-indexer script
       Provides command-line functions to create, update and delete
       indexes. Provides also a simple search functionality intended for
       debugging purposes mainly.

AUTHORS
   Copyright (c) 2005 Andrew Maltsev

   Copyright (c) 2003-2004 Andrew Maltsev, XAO Inc.

   <[email protected]> -- http://ejelta.com/xao/

SEE ALSO
   Recommended reading: XAO::DO::Data::Index, XAO::DO::Indexer::Base,
   XAO::FS, XAO::Web.

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