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libexttextcat is an N-Gram-Based Text Categorization library primarily intended
for language guessing.

Fundamentally this is an adaption of wiseguys libtextcat extended to be UTF-8
aware. See README.libtextcat for details on original libtextcat.

Building:

 * ./configure
 * make
 * make check

the tests can be run under valgrind's memcheck with export VALGRIND=memcheck,
e.g.

 * export VALGRIND=memcheck
 * make check

Quickstart: language guesser
  
 Assuming that you have successfully compiled the library, you need some
language models to start guessing languages. A collection of over 150 language
models, mostly derived from using the included "createfp" utility on UDHR
translations, is bundled, with a matching configuration file, in the langclass
directory:

  * cd langclass/LM
  * ../../src/testtextcat ../fpdb.conf
  	 
Paste some text onto the commandline, and watch it get classified.
     
Using the API:
  
Classifying the language of a textbuffer can be as easy as:

 #include "textcat.h"
 ...
 void *h = textcat_Init( "fpdb.conf" );
 ...
 printf( "Language: %s\n", textcat_Classify(h, buffer, 400);
 ...
 textcat_Done(h);
      
Creating your own fingerprints:
  
The createfp program allows you to easily create your own document
fingerprints. Just feed it an example document on standard input, and store the
standard output:

Put the names of your fingerprints in a configuration file, add some id's and
you're ready to classify.

Here's a worked example. The UN Declaration of Human Rights is available in a
massive pile of translations[4], and and unicode.org makes much of these
available as plain text[5], so...

% cd langclass/ShortTexts/
% wget http://unicode.org/udhr/d/udhr_abk.txt
% tail -n+7 udhr_abk.txt > ab.txt #skip english header, name is using BCP-47
% cd ../LM
% ../../src/createfp < ../ShortTexts/ab.txt > ab.lm
% echo "ab.lm       ab--utf8" >> ../fpdb.conf

Eventually we'll drop fpdb.conf and assume the name of the fingerprint .lm file
is the correct BCP-47 tag for the language it detects.
    
Performance tuning:

This library was made with efficiency in mind. There are couple of
parameters you may wish to tweak if you intend to use it for other
tasks than language guessing.

The most important thing is buffer size. For reliable language
guessing the classifier only needs a couple of hundreds of bytes max.
So don't feed it 100KB of text unless you are creating a fingerprint.

If you insist on feeding the classifier lots of text, try fiddling
with TABLEPOW, which determines the size of the hash table that is
used to store the n-grams. Making it too small will result in many
hashtable clashes, making it too large will cause wild memory
behaviour and both are bad for the performance.

Putting the most probable models at the top of the list in your config
file improves performance, because this will raise the threshold for
likely candidates more quickly.

Since the speed of the classifier is roughly linear with respect to
the number of models, you should consider how many models you really
need. In case of language guessing: do you really want to recognize
every language ever invented?

Acknowledgements

UTF-8 conversion and adaption for OpenOffice.org, Jocelyn Merand.
Original libTextCat, Frank Scheelen & Rob de Wit at wise-guys.nl.
Original language models, copyright Gertjan van Noord.

References:

[1] The document that started it all can be downloaded at John M.
Trenkle's site: N-Gram-Based Text Categorization

http://www.novodynamics.com/trenkle/papers/sdair-94-bc.ps.gz

[2] The Perl implementation by Gertjan van Noord (code + language
models): downloadable from his website

http://odur.let.rug.nl/~vannoord/TextCat/

[3] Original libtextcat implementation at

http://software.wise-guys.nl/libtextcat/

[4] http://www.ohchr.org/EN/UDHR/Pages/SearchByLang.aspx

[5] http://unicode.org/udhr/index_by_name.html

Contact:

Questions or patches can be directed to libreoffice@lists.freedesktop.org.
Bugs can be directed to https://bugs.freedesktop.org