Effect of Cross-Language IR in Bilingual Lexicon Acquisition from Comparable Corpora

Japanese News Articles DB English News Articles DB Relevant Article Pair 411W Phrase Alignment / Spottm *.„ •Bilingual Dictionary •MT System Translation Knowledge DB Translation Knowledge Acquisition } Retrieval of Bilingual Article Pair WWW (News Sites) Effect of Cross-Language IR in Bilingual Lexicon Acquisition from Comparable Corpora Takehito Utsuro� Takashi Horiuchi and Kohei Hino Graduate School of Informatics, Takeshi Hamamoto and Takeaki Nakayama Kyoto University�Dpt. Information and Computer Sciences, Sakyo-ku, Kyoto, 606-8501, Japan� Toyohashi University of Technology utsuro@i kyot o -u . ac. jp Tenpaku-cho, Toyohashi, 441-8580, Japan Abstract Within the framework of translation knowledge acquisition from WWW news sites, this paper studies issues on the effect of cross-language retrieval of relevant texts in bilingual lexicon ac- quisition from comparable corpora. We experimentally show that it is quite ef- fective to reduce the candidate bilingual term pairs against which bilingual term correspondences are estimated, in terms of both computational complexity and the performance of precise estimation of bilingual term correspondences. 1 Introduction Translation knowledge acquisition from paral- lel/comparative corpora is one of the most impor- tant research topics of corpus-based MT. This is because it is necessary for an MT system to (semi- )automatically increase its translation knowledge in order for it to be used in the real world situ- ation. One limitation of the corpus-based trans- lation knowledge acquisition approach is that the techniques of translation knowledge acquisition heavily rely on availability of parallel/comparative corpora. However, the sizes as well as the domain of existing parallel/comparative corpora are lim- ited, while it is very expensive to manually col- lect parallel/comparative corpora. Therefore, it is quite important to overcome this resource scarcity bottleneck in corpus-based translation knowledge acquisition research. In order to solve this problem, this paper fo- cuses on bilingual news articles on WWW news sites as a source for translation knowledge acqui- sition. In the case of WWW news sites in Japan, Figure 1: Translation Knowledge Acquisition from WWW News Sites: Overview Japanese as well as English news articles are up- dated everyday. Although most of those bilingual news articles are not parallel even if they are from the same site, certain portion of those bilingual news articles share their contents or at least re- port quite relevant topics. Based on this obser- vation, we take an approach of acquiring transla- tion knowledge of domain specific named entities, event expressions, and collocational expressions from the collection of bilingual news articles on WWW news sites (Utsuro and others, 2002). Figure 1 illustrates the overview of our frame- work of translation knowledge acquisition from WWW news sites. First, pairs of Japanese and En- glish news articles which report identical contents or at least closely related contents are retrieved. (Hereafter, we call pairs of bilingual news arti- cles which report identical contents as "identical" pair, and those which report closely related con- tents (e.g., a pair of a crime report and the arrest 355 of its suspect) as "relevant" pair.) Then, by ap- plying previously studied techniques of translation knowledge acquisition …

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