425 research outputs found
A Survey of Word Reordering in Statistical Machine Translation: Computational Models and Language Phenomena
Word reordering is one of the most difficult aspects of statistical machine
translation (SMT), and an important factor of its quality and efficiency.
Despite the vast amount of research published to date, the interest of the
community in this problem has not decreased, and no single method appears to be
strongly dominant across language pairs. Instead, the choice of the optimal
approach for a new translation task still seems to be mostly driven by
empirical trials. To orientate the reader in this vast and complex research
area, we present a comprehensive survey of word reordering viewed as a
statistical modeling challenge and as a natural language phenomenon. The survey
describes in detail how word reordering is modeled within different
string-based and tree-based SMT frameworks and as a stand-alone task, including
systematic overviews of the literature in advanced reordering modeling. We then
question why some approaches are more successful than others in different
language pairs. We argue that, besides measuring the amount of reordering, it
is important to understand which kinds of reordering occur in a given language
pair. To this end, we conduct a qualitative analysis of word reordering
phenomena in a diverse sample of language pairs, based on a large collection of
linguistic knowledge. Empirical results in the SMT literature are shown to
support the hypothesis that a few linguistic facts can be very useful to
anticipate the reordering characteristics of a language pair and to select the
SMT framework that best suits them.Comment: 44 pages, to appear in Computational Linguistic
How much hybridisation does machine translation need?
This is the peer reviewed version of the following article: [Costa-jussà, M. R. (2015), How much hybridization does machine translation Need?. J Assn Inf Sci Tec, 66: 2160–2165. doi:10.1002/asi.23517], which has been published in final form at [10.1002/asi.23517]. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.Rule-based and corpus-based machine translation (MT)have coexisted for more than 20 years. Recently, bound-aries between the two paradigms have narrowed andhybrid approaches are gaining interest from bothacademia and businesses. However, since hybridapproaches involve the multidisciplinary interaction oflinguists, computer scientists, engineers, and informa-tion specialists, understandably a number of issuesexist.While statistical methods currently dominate researchwork in MT, most commercial MT systems are techni-cally hybrid systems. The research community shouldinvestigate the bene¿ts and questions surrounding thehybridization of MT systems more actively. This paperdiscusses various issues related to hybrid MT includingits origins, architectures, achievements, and frustra-tions experienced in the community. It can be said thatboth rule-based and corpus- based MT systems havebene¿ted from hybridization when effectively integrated.In fact, many of the current rule/corpus-based MTapproaches are already hybridized since they do includestatistics/rules at some point.Peer ReviewedPostprint (author's final draft
Coupling hierarchical word reordering and decoding in phrase-based statistical machine translation
In this paper, we start with the existing idea of taking reordering rules automatically derived from syntactic representations, and applying them in a preprocessing step before translation to make the source sentence structurally more like the target; and we propose a new approach to hierarchically extracting these rules. We evaluate this, combined with a lattice-based decoding, and show improvements over stateof-the-art distortion models.Postprint (published version
Towards improving English-Latvian translation: a system comparison and a new rescoring feature
This paper presents a comparative study of two alternative approaches to statistical machine translation (SMT) and their application to
a task of English-to-Latvian translation. Furthermore, a novel feature intending to reflect the relatively free word order scheme of the
Latvian language is proposed and successfully applied on the n-best list rescoring step. Moving beyond classical automatic scores of
translation quality that are classically presented in MT research papers, we contribute presenting a manual error analysis of MT systems
output that helps to shed light on advantages and disadvantages of the SMT systems under consideration.Postprint (published version
Using linear interpolation and weighted reordering hypotheses in the moses system
This paper proposes to introduce a novel reordering model in the open-source Moses toolkit. The main idea is to provide
weighted reordering hypotheses to the SMT decoder. These hypotheses are built using a first-step Ngram-based SMT
translation from a source language into a third representation that is called reordered source language. Each hypothesis
has its own weight provided by the Ngram-based decoder. This proposed reordering technique offers a better and more
efficient translation when compared to both the distance-based and the lexicalized reordering. In addition to this reordering
approach, this paper describes a domain adaptation technique which is based on a linear combination of an specific indomain
and an extra out-domain translation models. Results for both approaches are reported in the Arabic-to-English
2008 IWSLT task. When implementing the weighted reordering hypotheses and the domain adaptation technique in the
final translation system, translation results reach improvements up to 2.5 BLEU compared to a standard state-of-the-art
Moses baseline system.Postprint (published version
Latest trends in hybrid machine translation and its applications
This survey on hybrid machine translation (MT) is motivated by the fact that hybridization techniques have become popular as they attempt to combine the best characteristics of highly advanced pure rule or corpus-based MT approaches. Existing research typically covers either simple or more complex architectures guided by either rule or corpus-based approaches. The goal is to combine the best properties of each type.
This survey provides a detailed overview of the modification of the standard rule-based architecture to include statistical knowl- edge, the introduction of rules in corpus-based approaches, and the hybridization of approaches within this last single category. The principal aim here is to cover the leading research and progress in this field of MT and in several related applications.Peer ReviewedPostprint (published version
N-gram-based statistical machine translation versus syntax augmented machine translation: comparison and system combination
In this paper we compare and contrast
two approaches to Machine Translation
(MT): the CMU-UKA Syntax Augmented
Machine Translation system (SAMT) and
UPC-TALP N-gram-based Statistical Machine
Translation (SMT). SAMT is a hierarchical
syntax-driven translation system
underlain by a phrase-based model and a
target part parse tree. In N-gram-based
SMT, the translation process is based on
bilingual units related to word-to-word
alignment and statistical modeling of the
bilingual context following a maximumentropy
framework. We provide a stepby-
step comparison of the systems and report
results in terms of automatic evaluation
metrics and required computational
resources for a smaller Arabic-to-English
translation task (1.5M tokens in the training
corpus). Human error analysis clarifies
advantages and disadvantages of the
systems under consideration. Finally, we
combine the output of both systems to
yield significant improvements in translation
quality.Postprint (published version
English-Latvian SMT: the challenge of translating into a free word order language
This paper presents a comparative study of two approaches to
statistical machine translation (SMT) and their application to
a task of English-to-Latvian translation, which is still an open
research line in the field of automatic translation.
We consider a state-of-the-art phrase-based SMT and an
alternative N-gram-based SMT systems. The major differences
between these two approaches lie in the distinct representations
of bilingual units, which are the components of the
bilingual model driving translation process and in the statistical
modeling of the translation context.
Latvian being a rather free word order language implies
additional difficulties to the translation process. We contrast
different reordering models and investigate how well they
deal with the word ordering issue.
Moving beyond automatic scores of translation quality
that are classically presented in MT research papers, we contribute
presenting a manual error analysis of MT systems output
that helps to shed light on advantages and disadvantages
of the SMT systems under consideration and identify the most
prominent source of errors typical for both SMT systems.Postprint (published version
Reordering in statistical machine translation
PhDMachine translation is a challenging task that its difficulties arise from several characteristics
of natural language. The main focus of this work is on reordering as one of
the major problems in MT and statistical MT, which is the method investigated in this
research. The reordering problem in SMT originates from the fact that not all the words
in a sentence can be consecutively translated. This means words must be skipped and
be translated out of their order in the source sentence to produce a fluent and grammatically
correct sentence in the target language. The main reason that reordering is
needed is the fundamental word order differences between languages. Therefore, reordering
becomes a more dominant issue, the more source and target languages are
structurally different.
The aim of this thesis is to study the reordering phenomenon by proposing new methods
of dealing with reordering in SMT decoders and evaluating the effectiveness of
the methods and the importance of reordering in the context of natural language processing
tasks. In other words, we propose novel ways of performing the decoding to
improve the reordering capabilities of the SMT decoder and in addition we explore
the effect of improving the reordering on the quality of specific NLP tasks, namely
named entity recognition and cross-lingual text association. Meanwhile, we go beyond
reordering in text association and present a method to perform cross-lingual text fragment
alignment, based on models of divergence from randomness.
The main contribution of this thesis is a novel method named dynamic distortion,
which is designed to improve the ability of the phrase-based decoder in performing
reordering by adjusting the distortion parameter based on the translation context. The
model employs a discriminative reordering model, which is combining several fea-
2
tures including lexical and syntactic, to predict the necessary distortion limit for each
sentence and each hypothesis expansion. The discriminative reordering model is also
integrated into the decoder as an extra feature. The method achieves substantial improvements
over the baseline without increase in the decoding time by avoiding reordering
in unnecessary positions.
Another novel method is also presented to extend the phrase-based decoder to dynamically
chunk, reorder, and apply phrase translations in tandem. Words inside the chunks
are moved together to enable the decoder to make long-distance reorderings to capture
the word order differences between languages with different sentence structures.
Another aspect of this work is the task-based evaluation of the reordering methods and
other translation algorithms used in the phrase-based SMT systems. With more successful
SMT systems, performing multi-lingual and cross-lingual tasks through translating
becomes more feasible. We have devised a method to evaluate the performance
of state-of-the art named entity recognisers on the text translated by a SMT decoder.
Specifically, we investigated the effect of word reordering and incorporating reordering
models in improving the quality of named entity extraction.
In addition to empirically investigating the effect of translation in the context of crosslingual
document association, we have described a text fragment alignment algorithm
to find sections of the two documents in different languages, that are content-wise related.
The algorithm uses similarity measures based on divergence from randomness
and word-based translation models to perform text fragment alignment on a collection
of documents in two different languages.
All the methods proposed in this thesis are extensively empirically examined. We have
tested all the algorithms on common translation collections used in different evaluation
campaigns. Well known automatic evaluation metrics are used to compare the
suggested methods to a state-of-the art baseline and results are analysed and discussed
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