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Bridget McInnes > UMLS-Similarity > UMLS::Similarity::lesk



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Module Version: 0.07   Source   Latest Release: UMLS-Similarity-1.49


UMLS::Similarity::lesk - Perl module for computing semantic relatedness of concepts in the Unified Medical Language System (UMLS) using the method described by Banerjee and Pedersen (2002).


  title={An Adapted Lesk Algorithm for Word Sense Disambiguation using WordNet}, 
  author={Banerjee and Pedersen},
  journal={Proceedings of the Third International Conference on Intelligent Text Processiong 
                   and Computational Linguistics},  
  address={Mexico City}


  use UMLS::Interface;
  use UMLS::Similarity::lesk;

  my $umls = UMLS::Interface->new(); 
  die "Unable to create UMLS::Interface object.\n" if(!$umls);

  my $lesk = UMLS::Similarity::lesk->new($umls);
  die "Unable to create measure object.\n" if(!$lesk);

  my $cui1 = "C0018563";
  my $cui2 = "C0037303";

  $ts1 = $umls->getTermList($cui1);
  my $term1 = pop @{$ts1};

  $ts2 = $umls->getTermList($cui2);
  my $term2 = pop @{$ts2};

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

  print "The similarity between $cui1 ($term1) and $cui2 ($term2) is $value\n";


This module computes the semantic relatedness of two concepts in the UMLS according to a method described by Banerjee and Pedersen(2002). The relatedness measure proposed by Banerjee and Pedersen is and adaptation of Lesk's dictionary-based word sense disambiguation algorithm.

--defraw option

This is a flag for the lesk measure. The definitions used are 'cleaned'. If the --defraw flag is set they will not be cleaned, and it will leave the definitions in their "raw" form. If the --defraw and --stem option use together, the --stem option will cancel the request for "raw" defintion which is set by --defraw.

--dictfile option

This is a dictionary file for the vector measure. It contains the 'definitions' of a concept which would be used in the relatedness computation. When this option is set, for the input pair, first find the CUIs or terms definition in the dictfile. If the --config option is set, will find the definition in dictfile and in UMLS. And then, the relatedness is computed by the combinition of UMLS and dictfile defintions.

If the --dictfile option is not set, the definiton will only come from the UMLS defintion by the --config option.

The input pair could be the following formats.

    1. cui1/term1 cui2/term2 
       without --dictfile option and without --config option, 
       use the UMLS definition of the default config file. 

    2. cui1/term1 cui2/term2  --dictfile ./sample/dictfile
       --dictfile option is set and without --config option, 
       definitions only come from dictfile. 

    3. cui1/term1 cui2/term2  --config ./sample/leskmeasure.config
       without --dictfile option, --config option is set, 
       definitions only come from UMLS by the config file. 

    4. cui1/term1 cui2/term2  --dictfile ./sample/dictfile --config ./sample/leskmeasure.config
       --dictfile option is set, --config option is set, 
       definitions come from dictfile and UMLS. If the associated term 
       for each CUI is defined in the dictfile, the associated terms' 
       definition are also included.  

Terms in the dictionary file use the delimiter : to seperate the terms and their definition. It allows multi terms in one concept. Please see the sample file at /sample/dictfile

--doubledef option

This a dictionary file for the vector measure. It contains the 'definitons' of a concept which could be used in the relatedness computation. When this option is defined, for each word in the definition, it uses the word's definition in the doubledef file.

    For example, the original defintion for 'cat' is,
    cat: a feline pet

    And then, the word vector for feline and pet in the doubledef file is:
    feline: small to medium-sized cats, cougar cheetah
    pet: cat dog bird fish

    The final definition for cat is to combine the original definition for cat, and
    then add the definition for feline(only add once) and pet.

    cat: a feline pet small to medium-sized cats cougar cheetah cat dog bird fish

Terms in the dictionary file use the delimiter : to seperate the terms and their definition. It has the same format with the dictfile. Please see the sample file at /sample/dictfile. We extract the definition from the WordNet by glossFinder. For the extraced file, we further parse each senses of the same word and obtain a complete definition of the word.

--compoundfile options

This is a compound word list for the vector measure. It defines the compound words which are treated as one word in the definitions. This must be used with the vector or lesk method.

    For example, the definition for iraq and france are:

    iraq : saddam hussein
    france : jacques chirac

    In the --compoundfile file, "saddam hussein" and "jacques chirac" are compounds:


    So, the compound words in the definition could be detected:

    iraq : saddam_hussein
    france : jacques_chirac

The lesk method searches the overlap of iraq and france definitions and get the lesk relatedness scores.

--config option

This is configure file for the lesk or vector measure. It defines the relationship, source and rela relationship. When compute the relatedness of a pair, find the corresponding relationshps and source by the config file.

--stoplist option

This is a word list file for the lesk measure. The words in the file should be removed from the definition. In the stop list file, each word is in the regular expression format. A stop word sample file is under the samples folder which is called stoplist-nsp.regex.

--stem option

This is a flag for the lesk measure. If we the --stem flag is set, the words of the definition are stemmed by the the Porter Stemming algorithm.


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


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

   use UMLS::Similarity::lesk;
   $measure = UMLS::Similarity::lesk->new($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 (UMLS-Interface).

If the 'new' method is unable to create the object, '$measure' would be undefined.

To find the semantic 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');


The UMLS-Interface package takes a configuration file to determine which sources and relations to use when obtaining the extended definitions. We call the definition used by the measure, the extended definition because this may include definitions from related concepts.

The format of the configuration file is as follows:

SABDEF :: <include|exclude> <source1, source2, ... sourceN>

RELDEF :: <include|exclude> <relation1, relation2, ... relationN>

The possible relations that can be included in RELDEF are: 1. all of the possible relations in MRREL such as PAR, CHD, ... 2. CUI which refers the concepts definition 3. ST which refers to the concepts semantic types definition 4. TERM which refers to the concepts associated terms

For example, if we wanted to use the definitions from MSH vocabulary and we only wanted the definition of the CUI and the definitions of the CUIs SIB relation, the configuration file would be:

SABDEF :: include MSH RELDEF :: include CUI, SIB

Note: RELDEF takes any of MRREL relations and two special 'relations':

      1. CUI which refers to the CUIs definition

      2. TERM which refers to the terms associated with the CUI

If you go to the configuration file directory, there will be example configuration files for the different runs that you have performed.

For more information about the configuration options please see the README.


perl(1), UMLS::Interface

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


  If you have any trouble installing and using UMLS-Similarity, 
  please contact us via the users mailing list :

  You can join this group by going to:

  You may also contact us directly if you prefer :

      Bridget T. McInnes: bthomson at 

      Ted Pedersen : tpederse at


  Bridget T McInnes <bthomson at>
  Siddharth Patwardhan <sidd at>
  Serguei Pakhomov <pakh0002 at>
  Ted Pedersen <tpederse at>
  Ying Liu <liux0395 at>


Copyright 2004-2011 by Bridget T McInnes, Siddharth Patwardhan, Serguei Pakhomov, Ying Liu and Ted Pedersen

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

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