GREAT: open source software for statistical machine translation

The final publication is available at Springer via http://dx.doi.org/10.1007/s10590-011-9097-6[EN] In this article, the first public release of GREAT as an open-source, statistical machine translation (SMT) software toolkit is described. GREAT is based on a bilingual language modelling approach for SMT, which is so far implemented for n-gram models based on the framework of stochastic finite-state transducers. The use of finite-state models is motivated by their simplicity, their versatility, and the fact that they present a lower computational cost, if compared with other more expressive models. Moreover, if translation is assumed to be a subsequential process, finite-state models are enough for modelling the existing relations between a source and a target language. GREAT includes some characteristics usually present in state-of-the-art SMT, such as phrase-based translation models or a log-linear framework for local features. 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Exploiting linguistically-enriched models of phrase-based statistical machine translation

This thesis presents the design and implementation of linguistically-informed models for statistical phrase-based machine translation. Using Koehn’s Pharaoh (2004), a state-of-the-art SMT system, and Moses (Hoang, 2006), a variant of the former which supports factored translation models, we have investigated two approaches: Combined Feature Models and Factored Models. While Combined Feature Models make use of concatenations of linguistic features to enrich their models, Factored Models view a token as a vector of factors, enabling to build relatively independent models for each factor. In the context of machine translation, both models were expected to enrich the existing surface word model with additional linguistic information. The research undertaken focused on finding ways to improve output translation quality for English-to-French and French-to-English translations from various standpoints. A better general readability and understandability of a generated document should be achieved mainly by ensuring the text fluency in the target language (syntactic correctness), its adequacy (use of adequate terminology) and its fidelity (semantic adequacy). These main goals were addressed by first of all analysing the Pharaoh’s current performance, and understanding language specific and model-related problems encountered. Several experiments were then performed using our two approaches, and their results were compared. Despite a few noted improvements in some of the linguistic issues discussed, notably fixed expression translation and part-of-speech ambiguity, major problems involving complex syntactic structures in the source language still posed a hard challenge to the approach of linguistically augmenting phrase-based statistical machine translation

Evaluating syntax-driven approaches to phrase extraction for MT

In this paper, we examine a number of different phrase segmentation approaches for Machine Translation and how they perform when used to supplement the translation model of a phrase-based SMT system. This work represents a summary of a number of years of research carried out at Dublin City University in which it has been found that improvements can be made using hybrid translation models. However, the level of improvement achieved is dependent on the amount of training data used. We describe the various approaches to phrase segmentation and combination explored, and outline a series of experiments investigating the relative merits of each method

Dependency relations as source context in phrase-based SMT

The Phrase-Based Statistical Machine Translation (PB-SMT) model has recently begun to include source context modeling, under the assumption that the proper lexical choice of an ambiguous word can be determined from the context in which it appears. Various types of lexical and syntactic features such as words, parts-of-speech, and supertags have been explored as effective source context in SMT. In this paper, we show that position-independent syntactic dependency relations of the head of a source phrase can be modeled as useful source context to improve target phrase selection and thereby improve overall performance of PB-SMT. On a Dutch—English translation task, by combining dependency relations and syntactic contextual features (part-of-speech), we achieved a 1.0 BLEU (Papineni et al., 2002) point improvement (3.1% relative) over the baseline

Accuracy-based scoring for phrase-based statistical machine translation

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A syntactic skeleton for statistical machine translation

We present a method for improving statistical machine translation performance by using linguistically motivated syntactic information. Our algorithm recursively decomposes source language sentences into syntactically simpler and shorter chunks, and recomposes their translation to form target language sentences. This improves both the word order and lexical selection of the translation. We report statistically significant relative improvementsof 3.3% BLEU score in an experiment (English!Spanish) carried out on an 800-sentence test set extracted from the Europarl corpus

Parallel Treebanks in Phrase-Based Statistical Machine Translation

Given much recent discussion and the shift in focus of the field, it is becoming apparent that the incorporation of syntax is the way forward for the current state-of-the-art in machine translation (MT). Parallel treebanks are a relatively recent innovation and appear to be ideal candidates for MT training material. However, until recently there has been no other means to build them than by hand. In this paper, we describe how we make use of new tools to automatically build a large parallel treebank and extract a set of linguistically motivated phrase pairs from it. We show that adding these phrase pairs to the translation model of a baseline phrase-based statistical MT (PBSMT) system leads to significant improvements in translation quality. We describe further experiments on incorporating parallel treebank information into PBSMT, such as word alignments. We investigate the conditions under which the incorporation of parallel treebank data performs optimally. Finally, we discuss the potential of parallel treebanks in other paradigms of MT

Using supertags as source language context in SMT

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