Bilingual Knowledge Acquisition from Korean-English Parallel Corpus Using Alignment

Bilingual Knowledge Acquisition from Korean-English Parallel Corpus Using Alignment Method ( Korean-English Alignment at Word and Phrase Level ) Jung H. Shin and Young S. Han* and Key-Sun Choi Department of Computer Science Korean Advanced Institute of Science and Technology Taejon, 305-701, Korea *Department of Computer Science Suwon University Kyungki, 445-743, Korea emaih j hshin @stissbs.kordic.re.kr Abstract This paper snggests a method to align Korean-English parallel corpus. '1?he structural dissimilarity between Korean and Indo-European languages requires more flexible measures to evaluate the alignment candidates between the bilin- gual units than is used to handle the pairs of Indo-European languages. The flexible measure is intended to capture the dependency between bilingual items that can occur in different units accord- ing to different ordering rules. The pro- posed method to accomplish Korean- English aligmnent takes phrases as an alignment unit that is a departure from the existing methods taking words as the unit. Phrasal alignment avoids the problem of alignment units and appease the problem of ordering mismatch. The parameters are estimated using the EM algorithm. The proposed alignment al- gorithm is based on dynamic program- ming. In the experimenl, s carried out on 253,000 English words and its Ko- rean translations the proposed method achived 68.7% in accuracy at phrase level and 89.2% in accuracy with the bilingual dictionary induced from the alignment. 'File result of the align- ment may lead to richer bilingual data than can be derived from only word- level aligments. 1 Introduction Studies on parallel corpus consisting of multilin- gum texts are often guided with the purpose to obtain linguistic resources such as bilingual dic- tionary, bilingual grammars (Wu 1995) and trans- lation examples. Parallel texts have t)roved to be useful not only in tile development of statistical The House i s ~ gradually disintegrating with age kuCThc") cip-un("lhmse-nomina[ case) seyweI-iC time"-nominal case)) hullekam-ey("fly" -adverbial case) ttal-a("folh)w "-subordinative case) cemchacek-ulo("gradually"-adverbial case) pwungkwiha-y("disintegrate"-subordinate case) ka-koCgo"-subordinative case) iss-taCis"-final ending) Figure 1: An example of typical Korean-English alignment. machine translation (Brown et al. 1993) but also in other applications such as word sense disana- biguation (Brown et al. 1991) and bilingnal lex- icography (Klavans and Tzoukermann 1990). As the parallel corpora become more and more ac- cessible, many researches based on the bilingual corpora are now encouraged that were once con- sidered impractical. Alignment as a study of parallel corpus refers to the process of establishing the correspondences between matching elements in parallel corpus. Alignment methods tend to approach the problem differently according to the alignment units the methods adopt. Of various alignment options, the alignlnent of word units is to compute a sequence of the matching pairs of words in a parallel corpus. Figure 1 show the aligned results of a paral- lel corpus that was originally paired in a sentence level. In figure 1, the right-hand side of pair-wise aligmnent is the corresponding Korean words. De- scribed in the parentheses on the right of each Ko- rean word are corresponding English meaning and syntactic functions of the word. …

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