parallel-tools

This is a collection of scripts for making it simple to search for (possible) translation equivalents of morphemes, words or phrases using multiparallel corpora, for instance the Bible.

Searching

Searches are split into two parts:

identifying sentences/verses in the source language(s) matching some criteria, specified using one or more regular expressions.
searching for words or character sequences in the target language(s) that correlate with the distribution of the sentences/verses found in step 1.

For instance, if we want to search for not yet in English (ISO 639-3: eng), the find_instances.py script can be used like this:

python3 find_instances.py -e ' not yet ' eng

This will create a (long) list that looks like this:

01001001:0:6
01001002:0:6
01001003:0:6
01001004:0:6
[...]
60001008:1:32
[...]
62003002:23:32
[...]

The first column is the sentence identifier (in the Bible: verse number), the second column is the number of occurrences of the search term in that sentence, and the third column is the number of times the verse was found in the language(s) used for the search (not all translations contain the same sentences, the major split in the Bible corpus being between the New Testament and the Old Testament).

Most verses contain zero instances of not yet, while e.g. verse 60001008 contains not yet in only 1 of 32 translations of that verse, and 62003002 contains not yet in 23 of 32 translations.

Note the spaces! What follows the -e argument is a regular expression, and in this case we are interested in two full tokens, not and yet. It is also possible to search for things like suffixes, including variants due to vowel harmony (note that there is only a space after the suffix):

python3 find_instances.py -e 'ss[aä] ' fin

The list can be passed to the find_equivalents.py script, which does the heavy work of finding translation equivalents in other languages.

Developing queries

You can use the -v option to find_instances.py to print out the instances found in context. For instance:

python3 find_instances.py -v -e 'dzangbwe' dig

This is useful as a sanity check to make sure you do not get a lot of unintended hits in the source/seed language.

Example

The first part of this command, using find_instance.py, extracts the number of instances of the pattern (in this case, the bigram not yet) in each sentence of the English translations. The second part, using find_equivalents.py, searches for words and bigrams in Indonesian, German and Digo that match the distribution of not yet.

python3 find_instances.py -e ' not yet ' eng | \
    python3 find_equivalents.py --features=words,bigrams,subsequences ind deu dig

You can also do the inverse, that is, search for something in English which corresponds to the average distribution of the word belum in Indonesian, the bigram noch nicht in German, and the morpheme dzangbwe in Digo:

python3 find_instances.py -e ' belum ' ind | \
    python3 find_instances.py -a -e ' noch nicht ' deu | \
    python3 find_instances.py -a -e 'dzangbwe' dig | \
    python3 find_equivalents.py --features=words,bigrams,subsequences eng

Note the flag -a in the last two calls to find_instances.py. This tells the program to combine the the German contexts with the ones from Indonesian, and then combine the Digo contexts with the combined Indonesian/German ones. We can of course also search for these individually:

python3 find_instances.py -e 'dzangbwe' dig | \
    python3 find_equivalents.py --features=words,bigrams,subsequences eng

Use of ISO codes assumes that /etc/parallel-tools contains the corpus path, for instance:

[default]

corpus_path=/data/paralleltext/bibles/corpus

It is also possible to specify filenames directly, instead of ISO codes.

Types of searches

The argument --features takes a comma-separated list which can combine the following types:

words
bigrams
prefixes
suffixes
subsequences

Note that subsequences also covers prefixes and suffixes, so there is no point combining these. If you only want to look at the end or beginning of words, specifying suffixes or prefixes can save time, however.

In the hits, underscore _ is used to indicate a word boundary.

Comparing expressions

You can also combine -v with -a to only display instances that also match the previous query. For instance, if you want manually look for plural markers in Swedish, you can start by selecting a suitable noun in English and searching for its equivalent. In this case, we start with the forms "snake" and "snakes" (regular expression: snakes?):

python3 find_instances.py -e ' snakes? ' eng | python3 find_equivalents.py --features=subsequences swe-x-bible-1917
    83.07  _orm
    46.80  _orm_
    35.06  orm_
    5.27  _ormar_
    4.57  _ormar

The root is (correctly) identified as "orm", with possible suffixes. To look at only the singular instances:

python3 find_instances.py -e ' snake ' eng | python3 find_instances.py -a -v -e ' orm' swe-x-bible-1917

And for the plural ones:

python3 find_instances.py -e ' snakes ' eng | python3 find_instances.py -a -v -e ' orm' swe-x-bible-1917

From which you could tentatively conclude that the suffix "-ar" is a plural marker for this noun in Swedish.

Displaying parallel verses

In addition to the above, it is also possible to use the show_parallel.py script to print a selection of parallel verses. For instance, the following prints the three shortest verses containing "snake" or "snakes" in English, from two specific translations.

python3 find_instances.py -e ' snakes? ' eng  | python3 show_parallel.py -s -n 3 eng-x-bible-newinternational swe-x-bible-1917

Performance

This benchmark consists of searching through 1698 Bible translations for sequences corresponding to Finnish character sequence "hyvä". The time depends crucially on what types of sequences we look for, and on the number of processors of the machine, for the numbers below a 12-core Xeon CPU with hyperthreading was used:

Words only: 69 seconds
Words and bigrams: 205 seconds

robertostling/parallel-tools