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WordNet::Similarity::pUser3Contributed Perl DocumeWordNet::Similarity::path(3)

NAME
       WordNet::Similarity::path - Perl	module for computing semantic
       relatedness of word senses by counting nodes in the noun	and verb
       WordNet 'is-a' hierarchies.

SYNOPSIS
	 use WordNet::Similarity::path;

	 use WordNet::QueryData;

	 my $wn	= WordNet::QueryData->new();

	 my $path = WordNet::Similarity::path->new($wn);

	 my $value = $measure->getRelatedness("car#n#1", "bus#n#2");

	 my ($error, $errorString) = $measure->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 by
       counting	the number of nodes along the shortest path between the	senses
       in the 'is-a' hierarchies of WordNet.  The path lengths include the end
       nodes.  For example, the	path between shrub#n#1 and tree#n#1 is
       shrub#n#1A -A woody_plant#n#1A -A tree#n#1.

       Since a longer path length indicate less	relatedness, the relatedness
       value returned is the multiplicative inverse of the path	length
       (distance) between the two concepts: relatednessA =A 1A /A distance.
       If the two concepts are identical, then the distance between them is
       one; therefore, their relatedness is also 1.  If	no path	is found, then
       a large negative	number is returned and an error	is generated (see
       "getError()").

       The following methods are defined:

       $path->getRelatedness()
	   Computes the	relatedness of two word	senses using a node counting
	   scheme.  The	relatedness score is inversely proportional to the
	   number of nodes along the shortest path between the two word
	   senses.

	   Parameters: two word	senses in "word#pos#sense" format.

	   Returns: Unless a problem occurs, the return	value is the
	   relatedness score, which belongs to the interval (0,	1].  If	no
	   path	exists between the two word senses, then a large negative
	   number is returned.	If an error occurs, then the error level is
	   set to non-zero and an error	string is created (see the description
	   of getError()).  Note: the error level will also be set to 1	and an
	   error string	will be	created	if no path exists between the words.

   Discussion
       If the two synsets being	compared are the same, then the	resulting
       relatedness score will be 1.  For exaple, the score for car#n#1 and
       car#n#1 is 1.

       Due to multiple inheritance in the WordNet taxonomies, it is possible
       for there to be a tie for the shortest path between synsets.  If	such a
       tie occurs, then	all of the paths that are tied will be printed to the
       trace string.

       The relatedness value returned by "getRelatedness()" is the
       multiplicative inverse of the path length between the two synsets
       (1/path_length).	 This has a slightly subtle effect: it shifts the
       relative	magnitude of scores.  For example, if we have the following
       pairs of	synsets	with the given path lengths:

	 synset1 synset2: 3
	 synset3 synset4: 4
	 synset5 synset6: 5

       We observe that the difference in the score for synset1-synset2 and
       synset3-synset4 is the same as for synset3-synset4 and synset5-synset6.
       When we take the	multiplicative inverse of them,	we get:

	 synset1 synset2: .333
	 synset3 synset4: .25
	 synset5 synset6: .2

       Now the difference between the scores for synset3-synset4 is less than
       the difference for synset1-synset2 and synset3-synset4.	This can have
       negative	consequences when computing correlation	coefficients.  It
       might be	useful to compute relatedness as max_distanceA -A path_length,
       where max_distance is the longest possible shortest path	between	two
       synsets.	 The original path length can be easily	determined by taking
       the multiplicative inverse of the returned relatedness score:
       1/scoreA	=A 1/(1/path_length)A =A path_length.  The computation of
       max_distance is left as an exercise for the reader.

       If two different	word senses (wps strings) are given as input to
       getRelatedness, but both	word senses belong to the same synset, then 1
       is returned (e.g., car#n#1 and auto#n#1 both belong to the same
       synset).

   Usage
       The semantic relatedness	modules	in this	distribution are built as
       classes that define 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 path measure,	we would have the following
       lines of	code in	the Perl program.

	  use WordNet::Similarity::path;
	  $measure = WordNet::Similarity::path->new($wn, '/home/sid/path.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 path
       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 semantic 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 behavior 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 specified 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 with the	name of	the module ON THE
       FIRST LINE of the file. For example, a configuration file for the path
       module will have	on the first line 'WordNet::Similarity::path'. 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.

       The module parses the configuration file	and recognizes the following
       parameters:

       trace
	   The value of	this parameter specifies the level of tracing that
	   should be employed for generating the traces. This value is an
	   integer equal to 0, 1, or 2.	If the value is	omitted, then the
	   default value, 0, is	used. A	value of 0 switches tracing off. A
	   value of 1 or 2 switches tracing on.	 A trace level of 1 means the
	   synsets are represented as word#pos#sense strings, while for	level
	   2, the synsets are represented as word#pos#offset strings.

       cache
	   The value of	this parameter specifies whether or not	caching	of the
	   relatedness values should be	performed.  This value is an integer
	   equal to  0 or 1.  If the value is omitted, then the	default	value,
	   1, is used. A value of 0 switches caching 'off', and	a value	of 1
	   switches caching 'on'.

       maxCacheSize
	   The value of	this parameter indicates the size of the cache,	used
	   for storing the computed relatedness	value. The specified value
	   must	be a non-negative integer.  If the value is omitted, then the
	   default value, 5,000, is used. Setting maxCacheSize to zero has the
	   same	effect as setting cache	to zero, but setting cache to zero is
	   likely to be	more efficient.	 Caching and tracing at	the same time
	   can result in excessive memory usage	because	the trace strings are
	   also	cached.	 If you	intend to perform a large number of
	   relatedness queries,	then you might want to turn tracing off.

       rootNode
	   The value of	this parameter indicates whether or not	a unique root
	   node	should be used.	In WordNet, there is no	unique root node for
	   the noun and	verb taxonomies. If this parameter is set to 1 (or if
	   the value is	omitted), then certain measures	(wup, path, lch, res,
	   lin,	and jcn) will "fake" a unique root node. If the	value is set
	   to 0, then no unique	root node will be used.	 If the	value is
	   omitted, then the default value, 1, is used.

SEE ALSO
       perl(1),	WordNet::Similarity(3),	WordNet::QueryData(3)

       http://www.cs.utah.edu/~sidd

       http://wordnet.princeton.edu

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

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

AUTHORS
	Ted Pedersen, University of Minnesota Duluth
	tpederse at d.umn.edu

	Siddharth Patwardhan, University of Utah, Salt Lake City
	sidd at	cs.utah.edu

	Jason Michelizzi, University of	Minnesota Duluth
	mich0212 at d.umn.edu

BUGS
       None.

       To report bugs, go to <http://groups.yahoo.com/group/wn-similarity>.

COPYRIGHT AND LICENSE
       Copyright (c) 2005, Ted Pedersen, Siddharth Patwardhan and Jason
       Michelizzi

       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.

       Note: a copy of the GNU General Public License is available on the web
       at <http://www.gnu.org/licenses/gpl.txt>	and is included	in this
       distribution as GPL.txt.

perl v5.24.1			  2008-03-27	  WordNet::Similarity::path(3)

NAME | SYNOPSIS | DESCRIPTION | CONFIGURATION FILE | SEE ALSO | AUTHORS | BUGS | COPYRIGHT AND LICENSE

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