Constrained Recombination in an Example-based Machine Translation System

Constrained Recombination in an Example-based Machine Translation System Monica Gavrila University of Hamburg, Faculty of Mathematics, Informatics and Natural Sciences Vogt-Koelln Str. 30, 22527, Hamburg, Germany gavrila@informatik.uni-hamburg.de Abstract Constraints in natural language process- ing play an important role. In this pa- per we show which impact (word-order) constraints have on the translation re- sults, when they are applied in the re- combination step of a linear EBMT sys- tem. Both the baseline EBMT system and the constrained one are implemented during this research. In the experiments we use two language-pairs (Romanian- English and Romanian-German), in both directions of translations. In these lan- guage constellations, Romanian, an in- flected language with Latin root, is consid- ered under-resourced. This aspect makes the process of translation even more chal- lenging. 1 Introduction Machine translation (MT), one of the most chal- lenging domains in Natural Language Processing (NLP), plays an important role in ensuring global communication. Documents in various domains need to be translated in a large combination of language-pairs. As quite often it is hard to find the right human translators, with the right domain- and language-knowledge, MT can be considered, at least for these cases, a solution. Less spoken languages have to overcome a ma- jor gap in language resources and tools, which all ensure the development of a good MT-system. Even more, some of these under-resourced lan- guages are highly inflected, with a more compli- cated grammar and often having linguistic phe- nomena which have been not encountered in pre- c⃝ 2011 European Association for Machine Translation. vious language combinations. On the other side, exactly for these languages, human translators are few or missing, so MT-systems are highly re- quired. Based mainly on the existence of a parallel cor- pus, which does not necessary have to include a large number of examples1, example-based ma- chine translation (EBMT) seems to be a solution for under-resourced languages. This MT approach, which has its start in Nagao’s work (Nagao, 1984), is essentially translation by analogy. The basic premise is that, if a previously translated sentence occurs again, the same translation is likely to be correct again. Constraints in natural language processing play an important role, such as in constraint-based grammars. Constraints usually restrict the possible values that a variable (or a feature) may take with respect to certain rules. In MT, they have been used for example in the SMT approach: (Canisius and van den Bosch, 2009), (Cao and Sumita, 2010). In this paper we explore how (word-order) con- straints can be used in a linear EBMT system. As we employ an under-resourced language (i.e. Ro- manian), we keep the systems as resource-free as possible. The algorithms are mainly based on sur- face forms and corpus statistics. That is why our EBMT systems borrow ideas only from the linear and template-based EBMT approaches. We investigate two language pairs: Romanian- English and Romanian-German, in both directions of translation. The under-resourced language we consider in this work is Romanian, as when start- ing this work not …

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