Zero Pronoun Resolution in a Machine Translation System by using Japanese to English Verbal Semantic Attributes.

Zero Pronoun Resolution in a Machine Translation System by using Japanese to English Verbal Semantic Attributes. Hiromi Nakaiwa and Satoru Ikehara NTT Network Information Systems Laboratories 1-2356 Take Yokosuka-Shi Kanagawa 238-03 Japan Abstract A method of anaphoral resolution of zero pronouns in Japanese language texts using the verbal semantic attributes is suggested. This method focuses attention on the semantic attributes of verbs and examines the context from the relationship between the semantic attributes of verbs governing zero pronouns and the semantic attributes of verbs governing their referents. The semantic attributes of verbs are created using 2 different viewpoints: dynamic characteristics of verbs and the relationship of verbs to cases. By using this method, it is shown that, in the case of translating newspaper articles, the major portion (93%) of anaphoral resolution of zero pronouns necessary for machine translation can be achieved by using only linguistic knowledge. Factors to be given special attention when incorporating this method into a machine translation system are examined, together with suggested conditions for the detection of zero pronouns and methods for their conversion. This study considers four factors that are important when implementing this method in a Japanese to English machine translation system: the difference in conception between Japanese and English expressions, the difference in case frame patterns between Japanese and English, restrictions by voice and restriction by translation structure. Implementation of the proposed method with due consideration of these points leads to a viable method for anaphoral resolution of zero pronouns in a practical machine translation system. 1 Introduction In all natural languages, components that can be easily deduced by the reader are frequently omitted f~om expressions in texts. In Japanese in particular, the subject and object are often omitted. These phenomena cause problems in machine translation because components not overtly indicated in the source language (i.e. Japanese) become mandatory elements in the target language (i.e. English). Thus, in Japanese to English Wanslation systems it becomes necessary to identify corresponding case elements omitted from the Japanese original (these are referred to as "zero pronouns") to be translated into English expressions. Therefore, the technique of zero pronoun resolution is an extremely important function. Several methods have been proposed with regard to this problem. Grotz et al. proposed the method of resolving definite noun phrases by using a centering algorithm. Kameyama expanded this concept by introducing property sharing constraints and applied it to zero pronoun resolution in Japanese. This method relies on the types of postpositional particle and whether there are any empathy- loaded verbs to exercise control over priority rankings for the focus of discourse segments. Yoshimoto suggested a method that uses topics from a dialogue. This method has focused attention on the characteristic of the Japanese language where the case for the sentence is determined by the type of postpositional particle (e.g. "ha" (pronounced "wa"), "ga", "wo" and "hi" indicate the theme, subject, direct object and indirect object respectively). The method uses case elements accompanied by the postpositional particle "ha" and case dements become …

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