Using GIZA++

En français

GIZA++ is a program for aligning words and sequences of words in sentence aligned corpora. If you have parallel corpus you can use GIZA++ to make bilingual dictionaries for Apertium (e.g. using ReTraTos) or lexical selection rules.

Compiling

git clone https://github.com/moses-smt/giza-pp
cd giza-pp
make
cp GIZA++-v2/GIZA++ /path/prefix/bin/
cp GIZA++-v2/plain2snt.out /path/prefix/bin/
cp GIZA++-v2/snt2cooc.out /path/prefix/bin/
cp GIZA++-v2/snt2plain.out /path/prefix/bin/
cp GIZA++-v2/trainGIZA++.sh /path/prefix/bin/
cp mkcls-v2/mkcls /path/prefix/bin/

The /path/prefix/bin is what you use as -external-bin-dir to moses, e.g. perl train-model.perl -external-bin-dir /path/prefix/bin

Troubleshooting

If you're running a case-insensitive file system (typical for Mac OS) you'll have to edit the file model3.cpp before compiling, since it outputs two files named foo.a3.final and foo.A3.final. So before compiling, change eg. lines 321--322:

      alignfile = Prefix + ".A3." + number ;
      test_alignfile = Prefix + ".tst.A3." + number ;

into something like

      alignfile = Prefix + ".AA3." + number ;
      test_alignfile = Prefix + ".tst.AA3." + number ;

Usage

Download your corpus, and convert into one sentence per line.

Use plain2snt.out to convert your corpus into GIZA++ format:

$ plain2snt.out sv-text.txt da-text.txt 
w1:sv-text w2:da-text
sv-text -> sv-text
da-text -> da-text

You may get some warnings about empty sentences like these:

WARNING: filtered out empty sentence (source: sv-text.txt 23 target: da-text.txt 0).
WARNING: filtered out empty sentence (source: sv-text.txt 34 target: da-text.txt 0).

if it is a large corpus you may get a lot of warnings... — if you have a lot of warnings, consider changing the corpus.

After you've done this, you should have a couple of .snt files and a couple of .vcb files.

Next you need to generate word classes, using mkcls:

$ mkcls -m2 -psv-text.txt -c50 -Vsv-text.vcb.classes opt >& mkcls1.log
$ mkcls -m2 -pda-text.txt -c50 -Vda-text.vcb.classes opt >& mkcls1.log

Now use GIZA++ to build your dictionary (-S is the source language, -T is the target language, -C is the generated aligned text file, and -o is the output file prefix):

$ GIZA++ -S sv-text.vcb -T da-text.vcb -C sv-text_da-text.snt -p0 0.98 -o dictionary >& dictionary.log

and wait... You can watch the log in dictionary.log... but the training is likely to take upwards of 10 hours (at most several days), so have something else planned.

The final alignment can be found in the file dictionary.A3.final

trainGIZA++.sh

Note: These changes only apply if you are not planning to use Moses

To use the trainGIZA++.sh script, you need to make a few changes before compiling:

In Makefile change:

CFLAGS_OPT = $(CFLAGS) -O3 -DNDEBUG -DWORDINDEX_WITH_4_BYTE -DBINARY_SEARCH_FOR_TTABLE

to:

CFLAGS_OPT = $(CFLAGS) -O3 -DNDEBUG -DWORDINDEX_WITH_4_BYTE

and in trainGIZA++.sh itself, change:

if( $# != 3 )

to:

if( $#argv != 3 )

See also

• Corpora
• ReTraTos
• Moses
• Mgiza – a more recent alternative to Giza++
• Learning rules from parallel and non-parallel corpora using Giza to make lex-sel rules

External links

• statmt.org: Factored training