NAME
WordNet::Similarity::lch - Perl module for computing semantic relatedness of word senses using the method described by Leacock and Chodorow (1998).
SYNOPSIS
use WordNet::Similarity::lch;
use WordNet::QueryData;
my $wn = WordNet::QueryData->new();
my $myobj = WordNet::Similarity::lch->new($wn);
my $value = $myobj->getRelatedness("car#n#1", "bus#n#2");
($error, $errorString) = $myobj->getError();
die "$errorString\n" if($error);
print "car (sense 1) <-> bus (sense 2) = $value\n";DESCRIPTION
This module computes the semantic relatedness of word senses according to a method described by Leacock and Chodorow (1998). This method counts up the number of edges between the senses in the 'is-a' hierarchy of WordNet. This value is then scaled by the maximum depth of the WordNet 'is-a' hierarchy. A relatedness value is obtained by taking the negative log of this scaled value.
USAGE
The semantic relatedness modules in this distribution are built as classes that expose the following methods: new() getRelatedness() getError() getTraceString()
See the WordNet::Similarity(3) documentation for details of these methods.
TYPICAL USAGE EXAMPLES
To create an object of the lch measure, we would have the following lines of code in the perl program.
use WordNet::Similarity::lch;
$measure = WordNet::Similarity::lch->new($wn, '/home/sid/lch.conf');The reference of the initialized object is stored in the scalar variable '$measure'. '$wn' contains a WordNet::QueryData object that should have been created earlier in the program. The second parameter to the 'new' method is the path of the configuration file for the lch measure. If the 'new' method is unable to create the object, '$measure' would be undefined. This, as well as any other error/warning may be tested.
die "Unable to create object.\n" if(!defined $measure);
($err, $errString) = $measure->getError();
die $errString."\n" if($err);To find the sematic relatedness of the first sense of the noun 'car' and the second sense of the noun 'bus' using the measure, we would write the following piece of code:
$relatedness = $measure->getRelatedness('car#n#1', 'bus#n#2');To get traces for the above computation:
print $measure->getTraceString();However, traces must be enabled using configuration files. By default traces are turned off.
CONFIGURATION FILE
The behaviour of the measures of semantic relatedness can be controlled by using configuration files. These configuration files specify how certain parameters are initialized within the object. A configuration file may be specififed as a parameter during the creation of an object using the new method. The configuration files must follow a fixed format.
Every configuration file starts the name of the module ON THE FIRST LINE of the file. For example, a configuration file for the lch module will have on the first line 'WordNet::Similarity::lch'. This is followed by the various parameters, each on a new line and having the form 'name::value'. The 'value' of a parameter is optional (in case of boolean parameters). In case 'value' is omitted, we would have just 'name::' on that line. Comments are supported in the configuration file. Anything following a '#' is ignored till the end of the line.
The module parses the configuration file and recognizes the following parameters:
(a) 'trace::' -- can take values 0, 1 or 2 or the value can be omitted, in which case it sets the trace level to 1. Trace level 0 implies no traces. Trace level 1 and 2 imply tracing is 'on', the only difference being the way in which the synsets are displayed in the traces. For trace level 1, the synsets are represented as word#pos#sense strings, while for level 2, the synsets are represented as word#pos#offset strings.
(b) 'cache::' -- can take values 0 or 1 or the value can be omitted, in which case it takes the value 1, i.e. switches 'on' caching. A value of 0 switches caching 'off'. By default caching is enabled.
SEE ALSO
perl(1), WordNet::Similarity(3), WordNet::QueryData(3)
http://www.d.umn.edu/~patw0006
http://www.cogsci.princeton.edu/~wn
http://www.ai.mit.edu/people/jrennie/WordNet
http://groups.yahoo.com/group/wn-similarity
AUTHORS
Siddharth Patwardhan, <patw0006@d.umn.edu>
Ted Pedersen, <tpederse@d.umn.edu>COPYRIGHT AND LICENSE
Copyright 2003 by Siddharth Patwardhan and Ted Pedersen
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.