# UMLS::Similarity::lch.pm
#
# This module is a copy of UMLS::Similarity::lch.pm version 0.01
# (used as is from Semantic::Similarity)
# (Updated 09/01/2009 -- Bridget)
#
# This module is a copy of Semantic::Similarity::lch.pm version 0.01
# (Updated 08/09/2004 -- Sid)
#
# Module implementing the semantic relatedness measure described 
# by Leacock and Chodorow (1998).
#
# Copyright (c) 2004-2009,
#
# Bridget T McInnes, University of Minnesota, Twin Cities
# bthomson at cs.umn.edu
#
# Siddharth Patwardhan, University of Utah, Salt Lake City
# sidd at cs.utah.edu
#
# Serguei Pakhomov, University of Minnesota, Twin Cities
# pakh002 at umn.edu
#
# Ted Pedersen, University of Minnesota, Duluth
# tpederse at d.umn.edu
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation; either version 2
# of the License, or (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to 
#
# The Free Software Foundation, Inc., 
# 59 Temple Place - Suite 330, 
# Boston, MA  02111-1307, USA.


package UMLS::Similarity::lch;

use strict;
use warnings;
use UMLS::Similarity;

use vars qw($VERSION);
$VERSION = '0.01';

my $debug = 0;

sub new
{
    my $className = shift;
    return undef if(ref $className);

    if($debug) { print STDERR "In UMLS::Similarity::lch->new()\n"; }

    my $interface = shift;

    my $self = {};
    
    # Initialize the error string and the error level.
    $self->{'errorString'} = "";
    $self->{'error'} = 0;
 
   # Bless the object.
    bless($self, $className);
    
    # The backend interface object.
    $self->{'interface'} = $interface;

    if(!$interface)
    {
	$self->{'errorString'} .= "\nError (UMLS::Similarity::lch->new()) - ";
	$self->{'errorString'} .= "An interface object is required.";
	$self->{'error'} = 2;
    }

    # The backend interface object.
    $self->{'interface'} = $interface;
    
    return $self;
}


sub getRelatedness
{
    my $self = shift;
    return undef if(!defined $self || !ref $self);
    my $concept1 = shift;
    my $concept2 = shift;

    my $interface = $self->{'interface'};

    my (@path) = $interface->findShortestPath($concept1, $concept2);

    my $version = $interface->version();

    my $depth = $interface->depth();
    
    my $score = 0;
    if($#path > -1) {
	$score = -1 * ( log ( ($#path+1)/(2*$depth) ) );
    }
    return $score
}

# Method to return recent error/warning condition
sub getError
{
    my $self = shift;
    return (2, "") if(!defined $self || !ref $self);

    if($debug) { print STDERR "In UMLS::Similarity::lch->getError()\n"; }

    my $dontClear = shift;
    my $error = $self->{'error'};
    my $errorString = $self->{'errorString'};

    if(!(defined $dontClear && $dontClear)) {
	$self->{'error'} = 0;
	$self->{'errorString'} = "";
    }
    $errorString =~ s/^\n//;

    return ($error, $errorString);
}

# Function to return the current trace string
sub getTraceString
{
    my $self = shift;
    return "" if(!defined $self || !ref $self);
    my $returnString = $self->{'traceString'};
    $self->{'traceString'} = "" if($self->{'trace'});
    $returnString =~ s/\n+$/\n/;
    return $returnString;
}


1;
__END__

=head1 NAME

UMLS::Similarity::lch - Perl module for computing semantic relatedness
of word senses using the method described by Leacock and Chodorow (1998). This
module is a taxonomy independent implementation of the algorithm.

=head1 SYNOPSIS

  use UMLS::Similarity::lch;

  use WordNet::Interface;

  my $interface = WordNet::Interface->new();

  my $myobj = UMLS::Similarity::lch->new($interface);

  my $cui1 = "C0005767";
  my $cui2 = "C0007634";

  my $value = $myobj->getRelatedness($cui1, $cui2);

  ($error, $errorString) = $myobj->getError();

  die "$errorString\n" if($error);

  print "Similarity (lch) : $cui1 <-> $cui2 = $value\n";

=head1 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 concepts in the backend
taxonomy.  This value is then scaled by the maximum depth of the
taxonomy. A relatedness value is obtained by taking the negative log
of this scaled value.

=head1 USAGE

The semantic relatedness modules in this distribution are built as classes
that expose the following methods:
  new()
  getRelatedness()
  getError()
  getTraceString()

See the UMLS::Similarity(3) documentation for details of these methods.

=head1 TYPICAL USAGE EXAMPLES

To create an object of the lch measure, we would have the following
lines of code in the perl program. 

   use UMLS::Similarity::lch;
   $measure = UMLS::Similarity::lch->new($interface);

The reference of the initialized object is stored in the scalar
variable '$measure'. '$interface' contains an interface object that
should have been created earlier in the program. The interface object
defines methods to access a backend taxonomy (such as UMLS, etc.). 

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 concept 'blood' (C0005767) and
the concept 'cell' (C0007634) using the measure, we would write
the following piece of code:

   $relatedness = $measure->getRelatedness('C0005767', 'C0007634');
  
To get traces for the above computation:

   print $measure->getTraceString();

However, traces must be enabled using configuration files. By default
traces are turned off.

=head1 SEE ALSO

perl(1), UMLS::Similarity(3)

http://www.cogsci.princeton.edu/~wn

http://www.ai.mit.edu/people/jrennie/WordNet

http://groups.yahoo.com/group/wn-similarity

=head1 AUTHORS

  Bridget T McInnes <bthomson@cs.umn.edu>
  Siddharth Patwardhan <sidd@cs.utah.edu>
  Serguei Pakhomov <pakhomov.serguei@mayo.edu>
  Ted Pedersen <tpederse@d.umn.edu>

=head1 COPYRIGHT AND LICENSE

Copyright 2004-2009 by Bridget T McInnes, Siddharth Patwardhan, 
Serguei Pakhomov and Ted Pedersen

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

=cut