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#!/usr/bin/perl |
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# -*- Mode: Cperl -*- |
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# $Basename: WAIT.pm $ |
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# $Revision: 1.7 $ |
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# Author : Ulrich Pfeifer |
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# Created On : Wed Nov 5 16:59:32 1997 |
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# Last Modified By: Ulrich Pfeifer |
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# Last Modified On: Tue Apr 16 23:28:52 2002 |
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# Language : CPerl |
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# Update Count : 8 |
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# Status : Unknown, Use with caution! |
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# |
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# (C) Copyright 1997, Ulrich Pfeifer, all rights reserved. |
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# |
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# |
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|
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package WAIT; |
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use XSLoader; |
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# require DynaLoader; |
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our $VERSION; |
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# @ISA = qw(DynaLoader); |
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|
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$VERSION = '2.000'; |
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|
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XSLoader::load 'WAIT', $VERSION; |
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|
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__END__ |
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|
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=head1 NAME |
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|
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WAIT - a rewrite of the freeWAIS-sf engine in Perl and XS |
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|
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=head1 SYNOPSIS |
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|
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A Synopsis is not yet available. |
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|
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=head1 Status of this document |
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|
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I started writing down some information about the implementation |
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before I forget them in my spare time. The stuff is incomplete at |
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least. Any additions, corrections, ... welcome. |
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|
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=head1 PURPOSE |
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|
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As you might know, I developed and maintained B<freeWAIS-sf> (with the |
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help of many people in The Net). FreeWAIS-sf is based on B<freeWAIS> |
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maintained by the Clearing House for Network Information Retrieval |
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(CNIDR) which in turn is based on B<wais-8-b5> implemented by Thinking |
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Machine et al. During this long history - implementation started about |
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1989 - many people contributed to the distribution and added features |
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not foreseen by the original design. While the system fulfills its |
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task now, the code has reached a state where adding new features is |
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nearly impossible and even fixing longstanding bugs and removing |
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limitations has become a very time consuming task. |
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|
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Therefore I decided to pass the maintenance to WSC Inc. and built a |
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new system from scratch. For obvious reasons I choosed Perl as |
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implementation language. |
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|
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=head1 DESCRIPTION |
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|
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The central idea of the system is to provide a framework and the |
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building blocks for any indexing and search system the users might |
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want to build. Obviously the framework limits the class of system |
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which can be build. |
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|
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+------+ +-----+ +------+ |
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==> |Access| ==> |Parse| ==> | | |
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+------+ +-----+ | | |
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|| | | +-----+ |
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|| |Filter| ==> |Index| |
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\/ | | +-----+ |
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+-------+ +-----+ | | |
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<= |Display| <== |Query| <-> | | |
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+-------+ +-----+ +------+ |
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|
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A collection (aka table) is defined by the instances of the B<access> |
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and B<parse> module together with the B<filter definitions>. At query |
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time in addition a B<query> and a B<display> module must be choosen. |
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|
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=head2 Access |
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|
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The access module defines which documents are members of a database. |
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Usually an access module is a tied hash, whose keys are the Ids of the |
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documents (did = document id) and whose values are the documents |
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themselves. The indexing process loops over the keys using C<FIRSTKEY> |
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and C<NEXTKEY>. Documents are retrieved with C<FETCH>. |
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|
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By convention access modules should be members of the |
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C<WAIT::Document> hierarchy. Have a look at the |
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C<WAIT::Document::Split> module to get the idea. |
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|
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|
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=head2 Parse |
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|
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The task of the parse module is to split the documents into logical |
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parts via the C<split> method. E.g. the C<WAIT::Parse::Nroff> splits |
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manuals piped through B<nroff>(1) into the sections I<name>, |
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I<synopsis>, I<options>, I<description>, I<author>, I<example>, |
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I<bugs>, I<text>, I<see>, and I<environment>. Here is the |
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implementation of C<WAIT::Parse::Base> which handles documents with a |
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pretty simple tagged format: |
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|
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AU: Pfeifer, U.; Fuhr, N.; Huynh, T. |
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TI: Searching Structured Documents with the Enhanced Retrieval |
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Functionality of freeWAIS-sf and SFgate |
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ER: D. Kroemker |
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BT: Computer Networks and ISDN Systems; Proceedings of the third |
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International World-Wide Web Conference |
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PN: Elsevier |
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PA: Amsterdam - Lausanne - New York - Oxford - Shannon - Tokyo |
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PP: 1027-1036 |
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PY: 1995 |
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|
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sub split { # called as method |
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my %result; |
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my $fld; |
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|
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for (split /\n/, $_[1]) { |
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if (s/^(\S+):\s*//) { |
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$fld = lc $1; |
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} |
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$result{$fld} .= $_ if defined $fld; |
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} |
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return \%result; |
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} |
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Since the original document cannot be reconstructed from its |
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attributes, we need a second method (I<tag>) which marks the regions |
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of the document with tags for the different attributes. This tagged |
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form is used by the display module to hilight search terms in the |
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documents. Besides the tags for the attributes, the method might assign |
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the special tags C<_b> and C<_i> for indicating bold and italic |
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regions. |
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|
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sub tag { |
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my @result; |
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my $tag; |
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|
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for (split /\n/, $_[1]) { |
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next if /^\w\w:\s*$/; |
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if (s/^(\S+)://) { |
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push @result, {_b => 1}, "$1:"; |
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$tag = lc $1; |
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} |
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if (defined $tag) { |
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push @result, {$tag => 1}, "$_\n"; |
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} else { |
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push @result, {}, "$_\n"; |
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} |
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} |
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return @result; # we don't go for speed |
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} |
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|
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Obviously one could implement C<split> via C<tag>. The reason for |
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having two functions is speed. We need to call C<split> for each |
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document when indexing a collection. Therefore speed is essential. On |
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the other hand, C<tag> is called in order to display a single document |
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and may be a little slower. It may care about tagging bold and italic |
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regions. See C<WAIT::Parse::Nroff> how this might decrease |
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performance. |
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|
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|
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=head2 Filter definition |
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|
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From the Information Retrieval perspective, the hardest part of the |
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system is the filter module. The database administrator defines for |
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each attribute, how the contents should be processed before it is |
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stored in the index. Usually the processing contains steps to restrict |
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the character set, case transformation, splitting to words and |
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transforming to word stems. In WAIT these steps are defined naturally |
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as a pipeline of processing steps. The pipelines are made up by |
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functions in the package B<WAIT::Filter> which is pre-populated by the |
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most common functions but may be extended any time. |
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The equivalent for a typical freeWAIS-sf processing would be this |
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pipeline: |
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[ 'isotr', 'isolc', 'split2', 'stop', 'Stem'] |
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|
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The function C<isotr> replaces unknown characters by blanks. C<isolc> |
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transforms to lower case. C<split2> splits into words and removes |
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words shorter than two characters. C<stop> removes the freeWAIS-sf |
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stopwords and C<Stem> applies the Porter algorithm for computing the |
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stem of the words. |
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|
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The filter definition for a collection defines a set of pipelines for |
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the attributes and modifies the pipelines which should be used for |
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prefix and interval searches. |
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|
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Several complete working examples come with WAIT in the script |
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directory. It is recommended to follow the pattern of the scripts |
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smakewhatis and sman. |
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|
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=cut |
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