bicleaner

Bicleaner (bicleaner-classify) is a tool in Python that aims at detecting noisy sentence pairs in a parallel corpus. It indicates the likelihood of a pair of sentences being mutual translations (with a value near to 1) or not (with a value near to 0). Sentence pairs considered very noisy are scored with 0.

Although a training tool (bicleaner-train) is provided, you may want to use the available ready-to-use language packages. Please, visit https://github.com/bitextor/bitextor-data/releases/tag/bicleaner-v1.0 to download the language packages.

Citation

If you find Bicleaner useful, please consider citing the following paper:

V. M. Sánchez-Cartagena, M. Bañón, S. Ortiz-Rojas and G. Ramírez-Sánchez,
"Prompsit's submission to WMT 2018 Parallel Corpus Filtering shared task",
in Proceedings of the Third Conference on Machine Translation, Volume 2: Shared Task Papers.
Brussels, Belgium: Association for Computational Linguistics, October 2018

@InProceedings{prompsit:2018:WMT,
  author    = { V\'{i}ctor M. S\'{a}nchez-Cartagena and Marta Ba{\~n}\'{o}n and Sergio Ortiz-Rojas and Gema Ram\'{i}rez-S\'{a}nchez},
  title     = {Prompsit's submission to WMT 2018 Parallel Corpus Filtering shared task},
  booktitle = {Proceedings of the Third Conference on Machine Translation, Volume 2: Shared Task Papers},
  month     = {October},
  year      = {2018},
  address   = {Brussels, Belgium},
  publisher = {Association for Computational Linguistics}
}

Installation & Requirements

Bicleaner works with Python 3.5 and can be instaled with pip:

python3.5 -m pip install bicleaner

Bicleaner requires the KenLM Python bindings with support for 7-gram language models. You can easily install them by running the following command, that will install the February 2019 version of KenLM with 7-gram support enabled.

python3.5 -m pip install https://github.com/vitaka/kenlm/archive/master.zip

If you need a more updated version, please clone KenLM from https://github.com/kpu/kenlm, edit the file setup.py, replace -DKENLM_MAX_ORDER=6 with -DKENLM_MAX_ORDER=7 and run:

python3.5 setup.py install

The remaining extra modules required by Bicleaner will be automatically downloaded and installed/upgraded (if required) with the first command.

After installation, four binary files (bicleaner-train, bicleaner-train-lite, bicleaner-classify and bicleaner-classify-lite) will be located in your python/installation/prefix/bin directory.

Cleaning

bicleaner-classify aims at detecting noisy sentence pairs in a parallel corpus. It indicates the likelihood of a pair of sentences being mutual translations (with a value near to 1) or not (with a value near to 0). Sentence pairs considered very noisy are scored with 0.

The input file (the parallel corpus to be classified) must contain at least four columns:

• col1: URL 1
• col2: URL 2
• col3: Source sentence
• col4: Target sentence

Any extra columns will be ignored.

The generated output file will contain the same lines and columns that the original input file had, adding an extra column containing the Bicleaner classifier score.

This tool can be run with

bicleaner-classify [-h] [--tmp_dir TMP_DIR] [-b BLOCK_SIZE]
                          [-p PROCESSES] [-d DISCARDED_TUS]
                          [--threshold THRESHOLD] [-q] [--debug]
                          [--logfile LOGFILE] [-S SL_TOKENIZER_PATH] [-T TL_TOKENIZER_PATH]
                          [--lm_threshold LM_THRESHOLD] [--keep_lm_result] [-v]
                          input [output] metadata

Parameters

• positional arguments:
  • input: Tab-separated files to be classified (line format: URL1 URL2 SOURCE_SENTENCE TARGET_SENTENCE [EXTRA_COLUMNS], tab-separated)
  • output: Output of the classification (default: standard output)
  • metadata: Training metadata (YAML file), generated by bicleaner-train or downloaded as a part of a language pack. You just need to untar the language pack for the pair of languages of the file you want to clean. The tar file contains a YAML metadata file.
• optional arguments:
  • -h, --help: show this help message and exit
• Optional:
  • --tmp_dir TMP_DIR: Temporary directory where creating the temporary files of this program (default: default system temp dir, defined by the environment variable TMPDIR in Unix)
  • -b BLOCK_SIZE, --block_size BLOCK_SIZE Sentence pairs per block (default: 10000)
  • -p PROCESSES, --processes PROCESSES: Number of processes to use (default: all CPUs minus one)
  • -d DISCARDED_TUS, --discarded_tus DISCARDED_TUS: TSV file with discarded TUs. Discarded TUs by the classifier are written in this file in TSV file. (default: None)
  • --threshold THRESHOLD: Threshold for classifier. If accuracy histogram is present in metadata, the interval for max value will be given as a default instead the current default. (default: 0.5)
  • -S SL_TOKENIZER_PATH: Source language tokenizer absolute path. If not given, Moses tokenizer is used.
  • -T TL_TOKENIZER_PATH: Target language tokenizer absolute path. If not given, Moses tokenizer is used.
  • --lm_threshold LM_THRESHOLD: Threshold for language model fluency scoring. All sentence pairs whose LM fluency score falls below the threshold are removed (classifier score set to 0), unless the option --keep_lm_result is set. (default: 0.5)
  • --keep_lm_result: Add an additional column to the results with the language model fluency score and do not set the classifier score to 0 for any sentence pair. (default: False)
• Logging:
  • -q, --quiet: Silent logging mode (default: False)
  • --debug: Debug logging mode (default: False)
  • --logfile LOGFILE: Store log to a file (default: <_io.TextIOWrapper name='' mode='w' encoding='UTF-8'>)
  • -v, --version: show version of this script and exit

Example

bicleaner-classify  \
        corpus.en-es.raw  \
        corpus.en-es.classifed  \
        training.en-es.yaml 

This will read the "corpus.en-es.raw" file, classify it with the classifier indicated in the "training.en-es.yaml" metadata file, writing the result of the classification in the "corpus.en-es.classified" file. Each line of the new file will contain the same content as the input file, adding a column with the score given by the Bicleaner classifier.

Automatic test

We included a small test corpus and a script to check that your Bicleaner classifier is working as expected. In order to use it, just run:

python3.5 -m pytest -s tests/bicleaner_test.py

This will download the required language pack, classify the provided test corpus, and check the resulting classification scores. If everything went as expected, the output will be "1 passed in XX.XX seconds". All downloaded data will be removed at the end of the testing session.

Training classifiers

In case you need to train a new classifier (i.e. because it is not available in the language packs provided at bitextor-data),

you can use bicleaner-train . bicleaner-train is a Python3 tool that allows you to train a classifier which predicts whether a pair of sentences are mutual translations or not and discards too noisy sentence pairs.

Requirements

In order to train a new classifier, you must provide:

• A clean parallel corpus (100k pairs of sentences is the recommended size)
• SL-to-TL and TL-to-SL probabilistic bilingual dictionaries. You can check their format by downloading any of the available language packs

Optionally, if you want the classifier to include an improved fluency filter based on language models, you must also provide:

• A monolingual corpus made ONLY of noisy sentences in the SL (100k sentences is the recommended size)
• A monolingual corpus made ONLY of noisy sentences in the TL (100k sentences is the recommended size)

Moreover, lmplz, the command to train a KenLM language model must be in PATH. See https://github.com/kpu/kenlm for instructions about its compilation and installation.

In principle, if you want to use Bicleaner to clean a partially noisy corpus, it could be difficult to find a corpus made solely of noisy sentences. Fortunately, Bicleaner contains a set of heuristic rules that can be used to extract very noisy sentences from a corpus.

Extracting noisy sentences from an existing corpus with heuristic rules

Given a parallel corpus, you can extract some of its noisiest sentences using heuristic rules by running the following command:

bicleaner-hardrules -s SOURCE_LANG -t TARGET_LANG --annotated_output OUTPUT_NOISY_FILE INPUT_FILE OUTPUT_ALL_FILE

where INPUT_FILE contains a sentence-aligned parallel corpus, with a sentence pair per line. Sentences are split by tab. OUTPUT_NOISY_FILE will contain only the noisy sentence pairs, with an additional column specifying the heuristic rule applied and OUTPUT_ALL_FILE will contain all the input sentences. They noisy ones will contain an additional column with the word "discard".

You can them obtain the monolingual noisy corpora by "cutting" the appropriate column:

cut -f 1 OUTPUT_NOISY_FILE > MONOLINGUAL_NOISY.SOURCE_LANG
cut -f 2 OUTPUT_NOISY_FILE > MONOLINGUAL_NOISY.TARGET_LANG

Parameters

It can be used as follows. Note that the parameters --noisy_examples_file_sl, --noisy_examples_file_tl, --lm_file_sl, --lm_file_tl, are mandatory if you want to enable improved fluency filter based on language models (recommended).

 bicleaner-train [-h] -m METADATA -c CLASSIFIER -s SOURCE_LANG -t
                          TARGET_LANG -d SOURCE_DICTIONARY -D
                          TARGET_DICTIONARY [--normalize_by_length]
                          [--treat_oovs] [--qmax_limit QMAX_LIMIT]
                          [--disable_features_quest] [-g GOOD_EXAMPLES]
                          [-w WRONG_EXAMPLES]
                          [--good_test_examples GOOD_TEST_EXAMPLES]
                          [--wrong_test_examples WRONG_TEST_EXAMPLES]
                          [--classifier_type {svm,nn,nn1,adaboost,random_forest}]
                          [--dump_features DUMP_FEATURES] [-b BLOCK_SIZE]
                          [-p PROCESSES]
                          [--wrong_examples_file WRONG_EXAMPLES_FILE] [-S SL_TOKENIZER_PATH] [-T TL_TOKENIZER_PATH] 
                          [--noisy_examples_file_sl NOISY_EXAMPLES_FILE_SL]
                          [--noisy_examples_file_tl NOISY_EXAMPLES_FILE_TL]
                          [--lm_dev_size LM_DEV_SIZE] [--lm_file_sl LM_FILE_SL]
                          [--lm_file_tl LM_FILE_TL]
                          [-q] [--debug] [--logfile LOGFILE]
                          [input]

• positional arguments:
  • input: Tab-separated bilingual input file (default: Standard input)(line format: SOURCE_SENTENCE TARGET_SENTENCE, tab-separated)
• optional arguments:
  • -h, --help: show this help message and exit
• Mandatory:
  • -m METADATA, --metadata METADATA: Training metadata (YAML file)
  • -c CLASSIFIER, --classifier CLASSIFIER: Classifier data file that will be created after training. This file should be placed in the same directory as the YAML training metadata, as they are usually distributed together.
  • -s SOURCE_LANG, --source_lang SOURCE_LANG: Source language code
  • -t TARGET_LANG, --target_lang TARGET_LANG: Target language code
  • -d SOURCE_DICTIONARY, --source_dictionary SOURCE_DICTIONARY: LR gzipped probabilistic dictionary
  • -D TARGET_DICTIONARY, --target_dictionary TARGET_DICTIONARY: RL gzipped probabilistic dictionary
• Options:
  • --noisy_examples_file_sl NOISY_EXAMPLES_FILE_SL: File with noisy sentences in the SL
  • --noisy_examples_file_tl NOISY_EXAMPLES_FILE_TL: File with noisy sentences in the TL
  • --lm_file_sl LM_FILE_SL: Output file with the created SL language model. This file should be placed in the same directory as the YAML training metadata, as they are usually distributed together.
  • --lm_file_tl LM_FILE_TL: Output file with the created TL language model. This file should be placed in the same directory as the YAML training metadata, as they are usually distributed together.
  • --lm_dev_size SIZE: Number of sentences to be removed from clean text before training LMs. These are used to estimate the perplexity of clean text. (default: 2000)
  • --normalize_by_length: Normalize by length in qmax dict feature
  • --treat_oovs: Special treatment for OOVs in qmax dict feature
  • --qmax_limit: Number of max target words to be taken into account, sorted by length (default: 20)
  • --disable_features_quest: Disable less important features
  • -g GOOD_EXAMPLES, --good_examples GOOD_EXAMPLES: Number of good examples (default: 50000)
  • -w WRONG_EXAMPLES, --wrong_examples WRONG_EXAMPLES: Number of wrong examples (default: 50000)
  • --good_test_examples GOOD_TEST_EXAMPLES: Number of good test examples (default: 2000)
  • --wrong_test_examples WRONG_TEST_EXAMPLES: Number of wrong test examples (default: 2000)
  • --classifier_type {svm,nn,nn1,adaboost,random_forest}: Classifier type (default: random_forest)
  • --dump_features DUMP_FEATURES: Dump training features to file (default: None)
  • -b BLOCK_SIZE, --block_size BLOCK_SIZE: Sentence pairs per block (default: 10000)
  • -p PROCESSES, --processes PROCESSES: Number of process to use (default: all CPUs minus one)
  • -S SL_TOKENIZER_PATH: Source language tokenizer absolute path. If not given, Moses tokenizer is used.
  • -T TL_TOKENIZER_PATH: Target language tokenizer absolute path. If not given, Moses tokenizer is used.
  • --wrong_examples_file WRONG_EXAMPLES_FILE: File with wrong examples extracted to replace the synthetic examples from method used by default (default: None)
• Logging:
  • -q, --quiet: Silent logging mode (default: False)
  • --debug: Debug logging mode (default: False)
  • --logfile LOGFILE: Store log to a file (default: <_io.TextIOWrapper name='' mode='w' encoding='UTF-8'>)

Example

bicleaner-train \
          corpus.en-cs.train\
          --treat_oovs \
          --normalize_by_length \
          -s en \
          -t cs \
          -d dict-en.gz \
          -D dict-cs.gz \
          -b  1000 \
          -c en-cs.classifier \
          -g 50000 \
          -w 50000 \
          -m training.en-cs.yaml \
          --classifier_type random_forest

This will train a Random Forest classifier for English-Czech using the corpus corpus.en-cs.train and the probabilistic dictionaries dict-en.gz and dict-cs.gz. This training will use 50000 good and 50000 bad examples, and a block size of 1000 sentences. The classifier data will be stored in en-cs.classifier, with the metadata in training.en-cs.yaml. The improved fluency language model filter will not be included.

The generated .yaml file provides the following information, that is useful to get a sense on how good or bad was the training (and is also a needed input file for classifying):

classifier: en-cs.classifier
classifier_type: random_forest
source_lang: en
target_lang: cs
source_dictionary: dict-en.gz
target_dictionary: dict-cs.gz
normalize_by_length: True
treat_oovs: True
qmax_limit: 20
disable_features_quest: True
good_examples: 50000
wrong_examples: 50000
good_test_examples: 2000
wrong_test_examples: 2000
good_test_histogram: [0, 2, 18, 83, 217, 450, 1596, 7245, 389, 0]
wrong_test_histogram: [3, 3114, 3949, 2309, 516, 86, 22, 1, 0, 0]
precision_histogram: [0.5000000, 0.5000750, 0.5922635, 0.7728047, 0.9406006, 0.9888651, 0.9975143, 0.9998690, 1.0000000, nan]
recall_histogram: [1.0000000, 1.0000000, 0.9998000, 0.9980000, 0.9897000, 0.9680000, 0.9230000, 0.7634000, 0.0389000, 0.0000000]
accuracy_histogram: [0.5000000, 0.5001500, 0.6557500, 0.8523000, 0.9636000, 0.9785500, 0.9603500, 0.8816500, 0.5194500, 0.5000000]
length_ratio: 0.9049934

Lite versions

Although bicleaner-train and bicleaner-classify make use of parallelization by distributing workload to the available cores, some users might prefer to implement their own parallelization strategies. For that reason, single-thread versions of Bicleaner scripts are provided: bicleaner-train-lite and bicleaner-classify-lite. The usage is exactly the same as for the full versions, but omitting the blocksize (-b) and processes (-p) parameter.