Constraint-based lexical selection module

Lexical transfer

This is the output of lt-proc -b on an ambiguous bilingual dictionary.

[74306] ^El<det><def><f><sg>/The<det><def><f><sg>$ 
^estació<n><f><sg>/season<n><sg>/station<n><sg>$ ^més<preadv>/more<preadv>$ 
^plujós<adj><f><sg>/rainy<adj><sint><f><sg>$ 
^ser<vbser><pri><p3><sg>/be<vbser><pri><p3><sg>$ 
^el<det><def><f><sg>/the<det><def><f><sg>$ 
^tardor<n><f><sg>/autumn<n><sg>/fall<n><sg>$^,<cm>/,<cm>$ 
^i<cnjcoo>/and<cnjcoo>$ ^el<det><def><f><sg>/the<det><def><f><sg>$ 
^més<preadv>/more<preadv>$ ^sec<adj><f><sg>/dry<adj><sint><f><sg>$ 
^el<det><def><m><sg>/the<det><def><m><sg>$ 
^estiu<n><m><sg>/summer<n><sg>$^.<sent>/.<sent>$

I.e.

L'estació més plujós és el tardor, i la més sec el estiu

Goes to:

The season/station more rainy is the autumn/fall, and the more dry the summer.

The module requires VM for transfer, or another apertium transfer implementation without lexical transfer in order to work.

Rule format

A rule is made up of:

• An action (select, remove)
• A "centre" (the source language token that will be treated)
• A target language pattern on which the action takes place
• A source language context

<rule>  
  <skip lemma="el"/>  
  <select lemma="dona" tags="n.*">    
    <acception lemma="wife"/> 
  </select>  
  <skip lemma="de"/>
</rule>

<pre>
<rule>  
  <select lemma="estació" tags="n.*">    
    <acception lemma="season"/> 
  </select>  
  <skip lemma="més"/>
  <skip lemma="plujós"/>
</rule>

<rule>  
  <skip lemma="guanyador"/>
  <skip lemma="de"/>
  <skip/>
  <select lemma="prova" tags="n.*">    
    <acception lemma="event"/> 
  </select>  
</rule>

Usage

$ cat /tmp/test | python apertium-lex-rules.py rules.txt 2>/dev/null
^El<det><def><f><sg>/The<det><def><f><sg>$ 
^estació<n><f><sg>/season<n><sg>$ ^més<preadv>/more<preadv>$ ^plujós<adj><f><sg>/rainy<adj><sint><f><sg>$ 
^ser<vbser><pri><p3><sg>/be<vbser><pri><p3><sg>$ ^el<det><def><f><sg>/the<det><def><f><sg>$ 
^tardor<n><f><sg>/autumn<n><sg>/fall<n><sg>$^,<cm>/,<cm>$ ^i<cnjcoo>/and<cnjcoo>$ ^el<det><def><f><sg>/the<det><def><f><sg>$ 
^més<preadv>/more<preadv>$ ^sec<adj><f><sg>/dry<adj><sint><f><sg>$ ^el<det><def><m><sg>/the<det><def><m><sg>$ 
^estiu<n><m><sg>/summer<n><sg>$ ^.<sent>/.<sent>$ 

With rules

$ cat /tmp/test | python apertium-lex-rules.py rules.txt | apertium-vm -c ca-en.t1x.vmb | apertium-vm -c ca-en.t2x.vmb |\
   apertium-vm -c ca-en.t3x.vmb | lt-proc -g ca-en.autogen.bin

The 
rainiest season 
is the 
autumn, and the 
driest the 
summer. 

With bilingual dictionary defaults

$ cat /tmp/test | apertium-lex-defaults ca-en.autoldx.bin | apertium-vm -c ca-en.t1x.vmb | apertium-vm -c ca-en.t2x.vmb |\
   apertium-vm -c ca-en.t3x.vmb | lt-proc -g ca-en.autogen.bin

The 
rainiest station 
is the 
autumn, and the 
driest the 
summer.

Rule application process

Optimal application

We're interested in the longest match, but not left to right, so what we do is make an automata of the rule contexts (one rule is one transducer, then we compose them), and we read through them, each state is an LU, It needs to be non-deterministic, and you keep a log of alive paths/states, but also their "weight" (how many transitions have been made) -- the longest for each of the ambiguous words is the winner when we get to the end of the sentence.

Writing and generating rules

Writing

A good way to start writing lexical selection rules is to take a corpus, and search for the problem word, you can then look at how the word should be translated, and the contexts it appears in.

Jacob's critique of the rule format

By 'skip' you actually means 'match'. And lemma selection should be called <select> :-)

So I'd write

<rule>  
  <match lemma="el"/>  
  <match lemma="dona" tags="n.*">  <select lemma="wife"/>  </match>
  <match lemma="de"/>
</rule>

and actually you would like to work on categories as well as lemmas.

Like, to prefer (human) beings and not things before "feel".

<rule>
  <match tags="n.*">  <select cat="beings"/>  </match>
  <match lemma="feel"/>
</rule>

--Jacob Nordfalk 12:22, 30 November 2011 (UTC)

Compiled

The general structure is as follows:

LSSRECORD = id, len, weight;

<ALPHABET>
<NUM_TRANSDUCERS>
<TRANSDUCER>
<TRANSDUCER>
<TRANSDUCER>
...
"main"
<TRANSDUCER>
<LSRRECORD>
<LSRRECORD>
<LSRRECORD>

Todo

• xml compiler
• compile rule operation patterns, as well as matching patterns
• make rules with gaps work
• optimal coverage

See also

• SVN Module: apertium-lex-tools