Countability and Number in Japanese to English Machine Translation

Countability and Number in Japanese to English Machine Translation Francis Bond, Kentaro Ogura, Satoru Ikehara NTT Communication Science Laboratories 1-2356 Take, YokosUka-shi, K~nagawa-ken, JAPAN 238-03 {bond,ogura,ikehara} @nttkb.ntt.jp Abstract This paper presents a heuristic method that uses information in the Japanese text along with knowledge of English countability and number stored in transfer dictionaries to de- termine the countability and number of En- glish.noun phrases. Incorporating this method into the machine translation system ALTJ/E, helped tO raise the percentage of noun phrases generated with correct use of articles and num- ber from 65% to 73%. 1 Introduction Correctly determining number is a difficult problem when translating from Japanese to English. This is because in Japanese, noun phrases are not normally marked with respect to number. Japanese nouns have no equivalent to the English singular and plural forms and verbs do not inflect to agree with the number of the subject (Kuno 1973). In addition, there is no grammatical marking of countability, t In order to generate English correctly, it is necessary to know whether a given noun phrase is countable or uncountable and, if countable, whether it is singular or plural. Deciding this is a problem even for humans translating from Japanese to English, but they have their own knowledge of both languages t Japanese does not have obligatory plural mor- phemes. Plurality can be marked but only rarely is, for example by adding a suffix such as tachi "and others" (this can normally only be used with people or mfimals). tO draw on. A machine translation system needs to have this knowledge codilied in some way. As generating articles and number is only important when the rest of the sentence has been correctly generated, them has not been a lot of research devoted to it. Recently, Murata and Nagao (1993) have proposed a method of determining the referentiality property and number of nouns in Japanese sentences for machine translation into English, but tim re- search has not yet been extended to include the actual English generation. This paper describes a method that extracts information relevant to countability and num- ber from the Japanese text and combines it with knowledge about countability and num- ber in English. First countability in English is discussed at the noun phrase and then the noun level. As a noun phrase's countability in English is affected by its referential property (generic, referential or ascriptive) we present a method of determining the referential use of Japanese noun phrases. Next the process of actually determining noun phrase countability and number is described. This is followed by some examples of sentences translated by the proposed method and a discussion of the results. The processing described in this paper has been implemented in NTI" Communication Science Laboratories' experimental machine translation system ALTJ/E ([kehara et al. 1991). Along with new processing for the generation of articles, wifich is not discussed in detail in this paper, it improved the percent- 32 age of noun phrases with correctly generated detemfiners and number flom …

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