Overview

This repository allow build models for machine translation (MT) quality estimation (QE). It is clearly Quest++ rip off that I made in order to experiment with 'before BERT' QE.

The data :

• English-German WMT18 sentences on the IT domain translated by in-house encoder-decoder attention-based NMT system (13,442 training and 1,000 development sentences)
• After running ./scripts/download-data.sh data will be downloaded to data/sentence-level/features/en_de.
• The usual 17 features used in WMT12-17 is considered for the baseline system
• WMT18 QE baseline model was SVM regression with an RBF kernel, with grid search algorithm for the optimisation of relevant parameters. I tried to reproduce this in config/svc.cfg

Train model

The program takes as an input; method, config file and additional parameters.

For example, to train model:

./quality_estimation.py --train --config config/svc.yaml

Preparing training corpora

To extract features from tsv file (needed columnt: src and trg):

./qulity_estimation.py --extract_features \
                       --src_lm_path data/lm.tok.en \
                       --trg_lm_path data/lm.tok.de \
                       --trg_ncount_path data/ngram-count.de \
                       -i input.tsv -i output.tsv

also remember to provide SRILM path either with export SRILM_PATH or by --srilm_path.

Available learning methods

All of available methods are taken from sklearn, so it is fairly easey to add other as well, but currently these are "supported":

• Support-Vector Machines (SVM). Documentation about classifier parameters is available at http://scikit-learn.org/stable/modules/generated/sklearn.svm.SVC.html#sklearn.svm.SVC. The parameters exposed in the "Parameters" section of the configuration file are:
  • C
  • coef0
  • kernel
  • degree
  • gamma
  • tol
  • verbose
• Decision Trees (DT). Documentation about classifier parameters is available at https://scikit-learn.org/stable/modules/generated/sklearn.tree.DecisionTreeClassifier.html. The parameters exposed in the "Parameters" section of the configuration file are:
  • ccp_alpha
  • criterion
• Multilayer Perceptron (MLP). Documentation about classifier parameters is available at https://scikit-learn.org/stable/modules/generated/sklearn.neural_network.MLPClassifier.html. The parameters exposed in the "Parameters" section of the configuration file are:
  • activation
  • alpha
  • epsilon
  • hidden_layer_sizes
  • learning_rate_init
  • max_iter -momentum

Feature selection

To set up a feature selection algorithm add the "feature_selection" section to the configuration file. This section is independent of the "learning" section:

feature_selection:
    method: LinearSVC
    parameters:
        cv: 10

learning:
    ...

Currently, the following feature selection algorithms are available:

• Linear Support Vector Classification. The exposed parameters are:
  • penalty (default=’l2’)
  • loss (default=’squared_hinge’)
  • dual (default=True)
  • tol (default=1e-4)
  • C (default=1.0)
  • fit_intercept (default=True)
  • intercept_scaling (default=1)
  • max_iterint (default=1000)

These parameters and the method are documented at: https://scikit-learn.org/stable/modules/generated/sklearn.svm.LinearSVC.html

Inference

To inference model on given input:

./quality_estimation.py --inference --config config/svc.yaml --input test.tsv