Translation Quality Estimation Tutorial
Hands-on QuEst++
Carolina Scarton and Lucia Specia
July 12, 2016
Abstract
In this tutorial we present QuEst++ , an open source framework forpipelined Translation Quality Estimation. QuEst++ is the newest version of QuEst, including several improvements into the core code and the
support to word and document-level feature extraction and machine learning. This framework has two modules: a Feature Extractor module anda Machine Learning module. With the two modules it is possible tobuild a full Quality Estimation system, that predicts the quality of unseen
data.

Contents
1 Introduction

1

2 QuEst++ : an Open Source Framework for Translation Quality
Estimation
3
2.1 Feature Extractor module . . . . . . . . . . . . . . . . . . . . . .
4
2.1.1 Including a feature . . . . . . . . . . . . . . . . . . . . . .
8
2.2 Machine Learning module . . . . . . . . . . . . . . . . . . . . . . 13
2.2.1 Adding a new algorithm . . . . . . . . . . . . . . . . . . . 14
3 License

16

4 Citation

16

1

Introduction

Quality Estimation (QE) of Machine Translation (MT) have become increasingly popular over the last decade. With the goal of providing a prediction on
the quality of a machine translated text, QE systems have the potential to makeMT more useful in a number of scenarios, for example, improving post-editing
efficiency by filtering out segments which would require more effort or time tocorrect than to translate from scratch [Specia, 2011], selecting high quality segments [Soricut and Echihabi, 2010], selecting a translation from either an MT
system or a translation memory [He et al., 2010], selecting the best translationfrom multiple MT systems [Shah and Specia, 2014], and highlighting words orphrases that need revision [Bach et al., 2011].
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Sentence-level QE is addressed as a supervised machine learning task using
a variety of algorithms to induce models from examples of sentence translations
annotated with quality labels (e.g. 1-5 likert scores). This level has been covered in shared tasks organised by the Workshop on Statistical Machine Translation (WMT) annually since 2012 [Callison-Burch et al., 2012, Bojar et al., 2013,
Bojar et al., 2014, Bojar et al., 2015]. While standard algorithms can be used
to build prediction models, key to this task is work of feature engineering.
Two open source feature extraction toolkits are available for that: Asiya1[Gonàlez et al., 2012] and QuEst2 [Specia et al., 2013]. The latter has beenused as the official baseline for the WMT shared tasks and extended by a number of participants, leading to improved results over the years.
Word-level
QE[Blatz et al., 2004,
Ueffing and Ney, 2005,
Luong et al., 2014] has recently received more attention. It is seemingly
a more challenging task where a quality label is to be produced for eachtarget word. An additional challenge is the acquisition of sizable training sets
Significant efforts have been made (including three years of shared task at
WMT), showing an increase on researches in word-level QE from last year.
An application that can benefit from word-level QE is spotting errors (wrong
words) in a post-editing/revision scenario.
Document-level QE has received much less attention than the other two levels. This task consists in predicting a single label for entire documents, be it
an absolute score [Scarton and Specia, 2014] or a relative ranking of translations by one or more MT systems [Soricut and Echihabi, 2010] (being useful for
gisting purposes, where post-editing is not an option). The first shared-task
on document-level QE was organised last year in WMT15. Although featureengineering is the focus of this tutorial, it is worth mentioning that one important research question in document-level QE is to define ideal quality labels for
documents [Scarton et al., 2015].
More recently, phrase-level QE has also been explored [Blain et al., 2016,
Logacheva and Specia, 2015]. The idea is to move from word-level and insteadof predicting the quality of single words, the quality of segments of words are
predicted. This is a very promising level with applications on improving postediting, building automatic post-editing systems and including information on
decoders. Phrase-level QE is being addressed for the first time in WMT16
shared task.3
QuEst++ 4 is a significantly refactored and expanded version of QuEst.
Feature extraction modules for both word and document-level QE were added
and sequence-labelling learning algorithms for word-level QE were made available. QuEst++ can be easily extended with new features at any textual level.
In this tutorial we present the two modules of QuEst++ : Feature
Extractor (implemented in Java) and Machine Learning (implemented in
Python) modules. In Section 2 both modules are presented. Section 2.1 contains details of the Feature Extractor module, including how to build and run
the system, how to add a new feature and how to extract the results. Section 2.2 presents the Machine Learning module, showing how to use the python
scripts and how to include a new scikit-learn [Pedregosa et al., 2011] algorithm
1 http://nlp.lsi.upc.edu/asiya/
2 http://www.quest.dcs.shef.ac.uk/
3 http://www.statmt.org/wmt16/quality-estimation-task.html
4 https://github.com/ghpaetzold/questplusplus

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in the code. Sections 3 and 4 contain the licence agreement and how to cite
QuEst++ , respectively.

2

QuEst++ : an Open Source Framework forTranslation Quality Estimation

In this section the basic functionalities of QuEst++ are shown. QuEst++ encompass a number of improvements and new functionalities over its previous
version. The main changes are listed below:• Refactoring of the core code of Feature Extractor module changes included:– Cleaning unused code in the main class.
– Creating ProcessorFactory classes in order to instantiate processorsclasses that are required by features (now, only processors that are
required are instantiated).
– Creating MissingResourcesGenerator classes in order to generatemissing resources (such as Language Model (LM) whenever it is possible).
• Implementing word and document-level features.
• Including a Conditional Random Fields (CRF) algorithm (by using CRFsuite) for word-level prediction.
• Changing the configuration file format.
Previous developers of QuEst can note the improvements in QuEst++ ,making the code cleaner and easier to understand. Users are benefited with amore understandable configuration file format, better documentation and elimination of unused dependencies.
In this section, we present how to use QuEst++ , how to build it and how
to add a new feature.
Download
For developers, QuEst++ can be downloaded from GitHub5 using the following
command:git clone https://github.com/ghpaetzold/questplusplus.git
For users, a stable version of QuEst++ is available at:
http://www.quest.dcs.shef.ac.uk
5 http://github.com

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System requirements• Java 86– NetBeans 8.17 OR– Apache Ant (>= 1.9.3)8• Python 2.7.69 (or above -only 2.7 stable distributions)– SciPy and NumPy (SciPy >=0.9 and NumPy >=1.6.1)10– scikit-learn (version 0.15.2)11– PyYAML12– CRFsuite13 (for word-level model only)
Please note: For Linux, the Feature Extractor Module should work withboth OpenJDK and Oracle versions (java-8-oracle14 recommended)
On Ubuntu, it’s easier to install Oracle distribution:
sudo apt-get install oracle-java8-installer(Checkhttp://ubuntuhandbook.org/index.php/2014/02/
install-oracle-java-6-7-or-8-ubuntu-14-04/ if you don’t find thatversion)
NetBeans has issues to build on Linux. Get Ant instead to build throughcommand line:
sudo apt-get install ant

2.1

Feature Extractor module

The feature extractor module is implemented in Java, as in the first versionof the framework. This module encompass over 150 implemented features forsentence-level, 40 features for word-level and 70 features for document-level.
This tutorial will cover baseline features only, although some information about
advanced features is provided.
Dependencies - tools
The dependencies for sentence and document-level baseline are:• Perl 515 (or above)
6 http://www.oracle.com/technetwork/java/javase/downloads/
jdk8-downloads-2133151.html
7 https://netbeans.org/downloads/
8 http://ant.apache.org/bindownload.cgi)
9 https://www.python.org/downloads/
10 http://www.scipy.org/install.html
11 https://pypi.python.org/pypi/scikit-learn/0.15.2
12 http://pyyaml.org/
13 http://www.chokkan.org/software/crfsuite/
14 http://www.oracle.com/technetwork/java/javase/downloads/
jdk8-downloads-2133151.html
15 https://www.perl.org/get.html

4• SRILM16• Tokenizer (available at lang_resources folder - from Moses toolkit17 )• Truecaser (available at lang_resources folder - from Moses toolkit)
Word-level features require the following libraries: Some of the libraries
required to compile and run the code are included in the lib directory in theroot directory of the distribution. The Java libraries should be included there
when possible. However, there are two libraries that were not included into thelib directory due their size (used for word-level features only):• Stanford Core NLP 3.5.1 models18 (stanford-corenlp-3.5.1-models.jar
only)• Stanford Core NLP Spanish models19
Advanced features (sentence and document-level) require the following tools:• TreeTagger20• Berkeley Parser21
Dependencies - resources
The resources required for sentence and document-level baseline features are:• corpus for source language• corpus for target language• LM for source language• LM for target language• ngram counts file for source language• ngram counts file for target language• Truecase model for source language• Truecase model for target language• Giza lex file
For word-level the resources required are:• corpus for source language• corpus for target language
16 http://www.speech.sri.com/projects/srilm/manpages/
17 http://www.statmt.org/moses/
18 http://nlp.stanford.edu/software/stanford-corenlp-full-2015-01-29.zip
19 http://nlp.stanford.edu/software/stanford-spanish-corenlp-2015-01-08-models.

jar
20 http://www.cis.uni-muenchen.de/\%7Eschmid/tools/TreeTagger/
21 https://github.com/slavpetrov/berkeleyparser

5• LM for source language• LM for target language• ngram counts file for source language• ngram counts file for target language• POS ngram counts file for source language• POS ngram counts file for target language• corpus com POS information for source language• corpus com POS information for target language• reference translations in the target language• stop words list of the source language• translation probabilities of the source language• Universal WordNet plugin22 (unzip this file inside the lang_resources
folder)Examples of these resources are provided in the lang_resources folder.
Resources for several languages can be downloaded from http://www.statmt.
org/wmt15/quality-estimation-task.html. Advanced features may require
specific data (please read the documentation of the specific features).
Input files
For word and sentence levels, the input files contain one sentence per line. For
document level, the input files contain paths to documents (one document perline). Both source and target files should have the same number of lines.
An alignment file should also be provided for word-level feature extraction.
This file is generated by Fast Align23 tool. Alternatively, we can provide thepath for the Fast Align tool on the configuration file and QuEst++ will generate
the missing resource.
Output file
The output file contain the features extracted separated by tab. Word-level features output are features templates for CRF algorithm. Sentence and documentlevel features are real values separated by tab.
22 http://resources.mpi-inf.mpg.de/yago-naga/uwn/uwn.zip
23 https://github.com/clab/fast_align6

Configuration file
Configuration file is a structured file (extension .properties) that contains information about the language pairs, featureset and paths to resources and tools.
An example of information about language pairs, featureset and source resourceis showed below:
sourceLang.default = spanish
targetLang.default = english
output= output/test
input= input/test
resourcesPath= ./lang_resources
featureConfig= config/features/features_blackbox_17.xml! Resources for source:
source.corpus = ./lang_resources/english/europarl-nc.en
source.lm= ./lang_resources/english/english_lm.lm
source.truecase.model = ./lang_resources/english/truecase-model.ensource.postagger= /export/tools/tree-tagger/cmd/tree-tagger-english
source.ngram= ./lang_resources/english/ngram-counts.europarl-nc.en.proc
source.tokenizer.lang= en
For running sentence and document-level baseline features, you need tochange the path to SRILM folder in your system:
tools.ngram.path= /export/tools/srilm/bin/i686-m64/

For word-level features, paths to SRILM, Fast Align and Universal WordNet
plugin should be changed accordingly:
tools.fast_align.path = /export/tools/fast-aligntools.ngram.path = /export/tools/srilm/bin/i686-m64/
tools.universalwordnet.path = ./lang_resources/uwn/

Feature configuration file
This is an XML file containing the features that should be extracted. The pathto this file is provided in the configuration file in the featureConfig parameter.
An example of this file is presented below:<?xml version="1.0" encoding="UTF-8" standalone="no"?><features><feature class="shef.mt.features.impl.bb.Feature1001"
description="number of tokens in the source sentence" index="1001"/><feature class="shef.mt.features.impl.bb.Feature1002"
description="number of tokens in the target sentence" index="1002"/><feature class="shef.mt.features.impl.bb.Feature1006"
description="average source token length" index="1006"/></features>
If this file is used, three features will be extracted by the Feature Extractor
module.
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BuildWe recommend the use of NetBeans (version 8.1)24 . Alternatively, you can
use Apache Ant (>= 1.9.3):
ant "-Dplatforms.JDK_1.8.home=/usr/lib/jvm/java-8-<<version>>"
The ant command will create all classes needed to use QuEst++ and a
QuEst++.jar file.
Basic Usage
The following commands run QuEst++ for word, sentence and document-levelfeature extraction, respectively (including data examples).
Word-level:java -cp QuEst++.jar:lib/* shef.mt.WordLevelFeatureExtractor-lang english spanish-input input/source.word-level.en input/target.word-level.es-alignments lang_resources/alignments/alignments.word-level.out-config config/config.word-level.properties
Sentence-level:java -cp QuEst++.jar shef.mt.SentenceLevelFeatureExtractor-tok -case true-lang english spanish-input input/source.sent-level.en input/target.sent-level.es-config config/config.sentence-level.properties
Document-level:java -cp QuEst++.jar shef.mt.DocLevelFeatureExtractor-tok -case true-lang english spanish-input input/source.sent-level.en input/target.sent-level.es-config config/config.sentence-level.properties
Omitting -tok option, the system will not tokenise the input. The option-case can be true, lower or none.
2.1.1

Including a feature

The following example provides basic steps to include a new feature at
QuEst++ . The example includes a feature at the sentence-level feature extractor. Similarly, features for word and document levels can be added.
Let’s include a feature that counts the number of complex words in a source
sentence and average it by the number of total words in the sentece. The source
language will be English and the target Spanish.
24 https://netbeans.org/downloads/

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Resources The first thing required is a resource, a list of simple words in
English. Our task will be to count how many words are out of this list. A listof simple words in English can be downloaded from:https://www.dropbox.com/s/vc2vbzs1w2yptni/list_simple_words?dl=0
Download the list and place it at lang_resources/english folder.
Processors Since our feature requires a resource, the second step is to createa processor that will read and store the data from the resource. Processor
classes are placed in the package shef.mt.tools (folder src/shef/mt/tools).
These classes are useful because they guarantee the modularity of the code.
Features do not contain read and store operations and more than one feature
can require the same processor (without the need of implementing the samecode twice). Moreover, the processors are instantiated only once for all featuresthat use them. Processors extends the ResourceProcessor class and implements the method processNextSentence (or processNextDocument). Thismethod is responsible to send information from the processor to the sentence
being evaluated. In order to read our list of simple words, let’s create a classcalled ComplexWordsProcessor.java in the package shef.mt.tools (folder
src/shef/mt/tools). This class should contain the code:
package shef.mt.tools;
import java.io.BufferedReader;import java.io.FileNotFoundException;
import java.io.FileReader;import java.io.IOException;
import java.util.ArrayList;
import java.util.logging.Level;
import java.util.logging.Logger;
import shef.mt.features.util.Doc;
import shef.mt.features.util.Sentence;
public class ComplexWordsProcessor
extends ResourceProcessor {private ArrayList<String> simpleWords;
public ComplexWordsProcessor(String path) {//Create hash of words:
this.simpleWords = new ArrayList<>();//Read and store words from file:try {BufferedReader reader =new BufferedReader(new FileReader(path));while(reader.ready()){
String word = reader.readLine().trim();this.simpleWords.add(word);}} catch (FileNotFoundException ex) {9

Logger.getLogger(StopWordsProcessor.class.getName()).log(Level.SEVERE, null, ex);} catch (IOException ex) {Logger.getLogger(StopWordsProcessor.class.getName()).log(Level.SEVERE, null, ex);}}
@Override
public void processNextSentence(Sentence s) {s.setValue("simplewords", this.simpleWords);}@Override
public void processNextDocument(Doc source) {throw new UnsupportedOperationException("Not supported yet.");}}This code assumes it will receive a valid path for a file witha word per line.
This class will be instantiated by the class
SentenceLevelProcessoFactory.java.
Feature Once we have create all processors required for the feature, the next
step is to implement the feature itself. Features classes are placed in theshef.mt.features.impl package (src/shef/mt/features/impl folder) andthey are named following a numerical order to group features (e.g. Feature1001
and Feature1002 are from the same group). These classes implements eachfeature, by using the resources provided by the processors. It extends the
Feature class and implement the method run that extracts the feature and set
the feature value for the sentece.25 Let’s create a class called Feature7001.java
in the shef.mt.features.impl.bb package (src/shef/mt/features/impl/bb
folder). This class should contain a code similar to:
package shef.mt.features.impl.bb;
import java.util.ArrayList;
import shef.mt.features.impl.Feature;import shef.mt.features.util.Sentence;
public class Feature7001 extends Feature {public Feature7001(){
this.setIndex(7001);
this.setDescription("Complex word count of source sentence");this.addResource("source.simplewords");}@Override
25 For word and document levels, the classes are WordLevelFeature and DocLevelFeature,

respectively.

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public void run(Sentence source, Sentence target) {ArrayList<String> simpleWords =(ArrayList<String>) source.getValue("simplewords");
String[] tokens = source.getTokens();
int complexWords = 0;
for (String token:tokens){
if (!simpleWords.contains(token)){complexWords+=1;}}//defining value for the feature
this.setValue(((float) complexWords)/tokens.length);}}
This class is assuming that the resource source.simplewords was provide
in the configuration file.
Feature configuration file A feature configuration file is a XML containing the featureset that will be extracted. These files are saved at theconfig/features folder. In order to run our new feature, let’s create a feature configuration file called features_complex_words.xml. This file should
contain:<feature class="shef.mt.features.impl.bb.Feature7001"
description="number of complex words in the source sentence"index="7001"/>
Configuration file The configuration file contains paths to the resources andtools that are used by QuEst++ . These files are in the config folder and havethe extension .properties In order to provide the path of the list of complex
words, we can include a line in the configuration file. This line should contain thename of the resource (that we gave in the feature file - source.simplewords).
Also, the featureConfig parameter should be changed to point to the newfeature configuration file.
featureConfig = config/features/features_complex_words.xml
source.simplewords = ./lang_resources/english/list_simple_words
SentenceLevelProcessoFactory This class is responsible for linking instantiated all required processors. It will search in the feature set provide for the
dependencies (resource or tools) required and it will instantiated the processors accordingly. This class is the link between the features requirements, theresource and tools paths in the configuration file and the processors. In its constructor there are if blocks checking for feature requirements. If a constructor
is required it is instantiated in a get method and added to the list of processorsthat will run for each sentence. The structure of this class is as follow://constructor
public SentenceLevelProcessorFactory(FeatureExtractor fe) {//Setup initial instance of ResourceProcessor matrix:
11this.resourceProcessors = null;//Setup feature extractor:
this.fe = fe;//Get required resources:
HashSet<String> requirements =fe.getFeatureManager().getRequiredResources();//Allocate source and target processor vectors:
ArrayList<ResourceProcessor> sourceProcessors =new ArrayList<ResourceProcessor>();ArrayList<ResourceProcessor> targetProcessors =new ArrayList<ResourceProcessor>();[IF BLOCKS checking for feature requirements]//Transform array lists in vectors:
ResourceProcessor[] sourceProcessorVector =new ResourceProcessor[sourceProcessors.size()];ResourceProcessor[] targetProcessorVector =new ResourceProcessor[targetProcessors.size()];sourceProcessorVector =(ResourceProcessor[]) sourceProcessors.toArray(sourceProcessorVector);
targetProcessorVector =(ResourceProcessor[]) targetProcessors.toArray(targetProcessorVector);//Return vectors:
this.resourceProcessors =new ResourceProcessor[][]{sourceProcessorVector, targetProcessorVector};}[GET Processor methods]
In order to implement our new feature, the following if block should be
added to the code.
if (requirements.contains("source.simplewords")){ComplexWordsProcessor complexWordsProcessor =this.getComplexWordsProcessor();sourceProcessors.add(complexWordsProcessor);}
The method getComplexWordsProcessor() should also be implemented:
private ComplexWordsProcessor getComplexWordsProcessor() {//Register resource:
ResourceManager.registerResource("source.simplewords");//Get paths to stop word lists:
String path = this.fe.getResourceManager().getProperty("source.simplewords");
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//Generate processors:
ComplexWordsProcessor processor = new ComplexWordsProcessor(path);//Return processors:
return processor;}
Build and Run Either build the system again using NetBeans or using
Apache Ant. Just run using the sentence-level basic usage line.

2.2

Machine Learning module

The machine learning module is implemented in Python and is located in thefolder learning of QuEst++ distribution. This module has support to several
algorithms from the scikit-learn toolkit and an implementation of CRF from
CRFsuite. Support to Gaussian Process (using GPy toolkit) needs update. Thistutorial presents how to run and how to add a new algorithm from scikit-learn
to the module.
Dependencies and Instalation
The program itself does not require any installation step, it is just a matter ofrunning it provided that all the system requirements for Python are installed.
Running
Note: Following commands are based on the assumption that all files are underlearning directory. The program takes only one input parameter, the configuration file. For example:
python src/learn_model.py config/svr.cfg
Please note that the file svr.cfg can be replaced by any other configuration
file for different algorithms.
For building CRF models for word-level QE, use:python src/learn_model_CRF.py config/crf.cfg
Configuration file
The configuration uses the YAML format. Its layout is quite straightforward. It
is formed by key and value pairs that map directly to dictionaries (in Python)or hash tables with string keys. One example is as follows:learning:
method: LassoLars
parameters:alpha: 1.0
max_iter: 500
normalize: True13

fit_intercept: True
fit_path: Trueverbose: False
Each keyword followed by a : represents an entry in a hash. In this example,
the dictionary contains an entry learning that points to another dictionary
with two entries method and parameters. The values of each entry can be lists,
dictionaries or primitive values like floats, integers, booleans or strings. Please
note that each level in the example above is indented with 4 spaces.
For more information about the YAML format please refer to http://www.
yaml.org/ .
The configuration file is composed of three main parts: input and generic
options, feature selection, and learning.
Input comprises the following four parameters:
x_train: data/features/wmt2012_qe_baseline/training.qe.baseline.tsv
y_train: data/features/wmt2012_qe_baseline/training.effort
x_test: data/features/wmt2012_qe_baseline/test.qe.baseline.tsv
y_test: data/features/wmt2012_qe_baseline/test.effort
The first two are the paths to the files containing the features for the training
set and the responses for the training set, respectively. The last two options referto the test dataset features and response values, respectively.
The format of the feature files is any format that uses a character to separate
the columns. The default is the tabulator char (tab) as this is the default format
generated by the features extractor module.
Two other options are available:
scale: true
separator: ’\t’
scale applies scikit-learn’s scale() function to remove the mean and divideby the unit standard deviation for each feature. This function is applied to theconcatenation of the training and test sets. More information about the scale
function implemented by scikit-learn can be found at http://scikit-learn.
org/dev/modules/generated/sklearn.preprocessing.scale.html.
separator sets the character used to delimit the columns in the input files.
For CRF algorithm a parameter related to the folder or the CRFsuite alsoneed to be set:
crfsuite: <<path-to-crfsuite>>
Configuration files for some of the implemented algorithms are available inthe config directory.
2.2.1

Adding a new algorithm

Let’s add a new algorithm from scikit-learn toolkit. In order to do this, we needto change the file learn_model.py (in the folder src). This file instantiates
and run all scikit-learn algorithms already implemented in the module. Not
only regression and classification is supported, but also different algorithms forfeature selection and several evaluation scores are already implemented.
14

The method that we need to change is called set_learning_method. In thismethod the scikit-learn algorithm is defined and all the parameters are passed.
Part of this method is presented below:
def set_learning_method(config, X_train, y_train):estimator = Nonelearning_cfg = config.get("learning", None)
if learning_cfg:
p = learning_cfg.get("parameters", None)o = learning_cfg.get("optimize", None)scorers = \set_scorer_functions(learning_cfg.get("scorer", [’mae’, ’rmse’]))method_name = learning_cfg.get("method", None)
if method_name == "SVR":
if o:tune_params = set_optimization_params(o)estimator = optimize_model(SVR(), X_train, y_train,
tune_params,
scorers,o.get("cv", 5),o.get("verbose", True),o.get("n_jobs", 1))elif p:estimator = SVR(C=p.get("C", 10),
epsilon=p.get(’epsilon’, 0.01),
kernel=p.get(’kernel’, ’rbf’),
degree=p.get(’degree’, 3),gamma=p.get(’gamma’, 0.0034),
tol=p.get(’tol’, 1e-3),
verbose=False)
else:
estimator = SVR()
It is possible to observe in the code that according to the o (optimise) andp (fixed parameters) options, the algorithm SVR is called differently. Thisparameters come from the configuration file.
To include the Linear Ridge algorithm from scikit-learn we need to add thefollowing code:
if method_name == "Ridge":
if o:tune_params = set_optimization_params(o)estimator = optimize_model(linear_model.Ridge(), X_train, y_train,
tune_params,
scorers,o.get("cv", 5),o.get("verbose", True),o.get("n_jobs", 1))15

elif p:estimator = linear_model.Ridge(alpha =0.5)
else:
estimator = linear_model.Ridge()
Also the following line should be add to the top of the learn_model.py file:from sklearn import linear_model
The next step is to create a configuration file for the new algorithm. Let’s
create a file called ridge.cfg inside the config folder. This file should follow
the YAML format, containing:x_train: data/features/wmt2012_qe_baseline/training.qe.baseline.tsv
y_train: data/features/wmt2012_qe_baseline/training.effort
x_test: data/features/wmt2012_qe_baseline/test.qe.baseline.tsv
y_test: data/features/wmt2012_qe_baseline/test.effort
scale: true
separator: "\t"learning:
method: Ridge
optimize:alpha: [0.1, 0.2, 0.3, 0.4, 0.5]scorer: [mae, rmse]
parameters:alpha: 0.5
Note that the parameter that should be optimised is alpha.
Run the system with the command line:
python src/learn_model.py config/ridge.cfg

3

LicenseThe license for the Java code and any python and shell scripts developed hereis the very permissive BSD License26 . For pre-existing code and resources, e.g.,scikit-learn, SRILM and Stanford parser, please check their websites.

4

Citation

Lucia Specia, Gustavo Henrique Paetzold and Carolina Scarton (2015): Multilevel Translation Quality Prediction with QuEst++. In Proceedings of ACLIJCNLP 2015 System Demonstrations, Denver, CO, pp. 118-125.27
26 http://en.wikipedia.org/wiki/BSD_licenses
27 http://aclweb.org/anthology/N/N15/N15-2016.pdf

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Acknowledgements
This particular release of QuEst++ was made possible through the EXPERT28(EU Marie Curie ITN No. 317471) project and funding from EAMT29 . We also
thank to QuEst30 (Pascal NoE), QTLaunchPad31 , QT2132 projects that fundedprevious versions of QuEst.

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