/ 
UMLS-Similarity-0.11
River stage one • 1 direct dependent • 1 total dependent
/ UMLS::Similarity::path

NAME

UMLS::Similarity::path - Perl module for computing semantic relatedness of concepts in the UMLS by simple edge counting.

SYNOPSIS

  use UMLS::Interface;
  use UMLS::Similarity::path;

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

  my $path = UMLS::Similarity::path->new($umls);
  die "Unable to create measure object.\n" if(!$path);
  
  my $cui1 = "C0005767";
  my $cui2 = "C0007634";
	
  @ts1 = $umls->getTermList($cui1);
  my $term1 = pop @ts1;

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

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

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

DESCRIPTION

If the concepts being compared are the same, then the resulting relatedness score will be 1. For example, the score for C0005767 and C0005767 is 1.

Due to multiple inheritance, 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:

concept1 concept2: 3
concept3 concept4: 4
concept5 concept6: 5

We observe that the difference in the score for concept1-concept2 and concept3-concept4 is the same as for concept3-concept4 and concept5-concept6. When we take the multiplicative inverse of them, we get:

concept1 concept2: .333
concept3 concept4: .25
concept5 concept6: .2

Now the difference between the scores for concept3-concept4 is less than the difference for concept1-concept2 and concept3-concept4. This can have negative consequences when computing correlation coefficients. It might be useful to compute relatedness as max_distance - path_length, where max_distance is the longest possible shortest path between two conceps. The original path length can be easily determined by taking the multiplicative inverse of the returned relatedness score: 1/score = 1/(1/path_length) = path_length.

If two different terms are given as input to getRelatedness, but both terms belong to the same concept, then 1 is returned (e.g., car and auto both belong to the same concept).

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.

TYPICAL USAGE EXAMPLES

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

use UMLS::Similarity::path;
$measure = UMLS::Similarity::path->new($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. 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 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.

SEE ALSO

perl(1), UMLS::Interface

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

CONTACT US

If you have any trouble installing and using UMLS-Similarity, 
please contact us via the users mailing list :
  
    umls-similarity@yahoogroups.com
   
You can join this group by going to:
  
    http://tech.groups.yahoo.com/group/umls-similarity/
   
You may also contact us directly if you prefer :
  
    Bridget T. McInnes: bthomson at cs.umn.edu 

    Ted Pedersen : tpederse at d.umn.edu

AUTHORS

Bridget T McInnes <bthomson at cs.umn.edu>
Siddharth Patwardhan <sidd at cs.utah.edu>
Serguei Pakhomov <pakh0002 at umn.edu>
Ted Pedersen <tpederse at d.umn.edu>

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.