Automatic Extraction of Aspectual Information from a Monolingual Corpus

Automatic Extraction of Aspectual Information from a Monolingual Corpus Akira Oishi Yuji Matsumoto Graduate School of Information Science Nara Institute of Science and TechnologT 8916-5 Takayama, Ikoma, Nara 630-01 Japan {ryo-o, matsu}~is, aist-nara, ac. j p Abstract This paper describes an approach to ex- tract the aspectual information of Japanese verb phrases from a monolingual corpus. We classify Verbs into six categories by means of the aspectual features which are defined on the basis of the possibility of co-occurrence with aspectual forms and ad- verbs. A unique category could be identi- fied for 96% of the target verbs. To evalu- ate the result of the experiment, we exam- ined the meaning of -leiru which is one of the most fundamental aspectual markers in Japanese, and obtained the correct recog- nition score of 71% for the 200 sentences. 1 Introduction Aspect refers to the internal temporal structure of events and is distinguished from tense, which has a deictic element in it, of reference to a point of time anchored by the speaker's utterance. There is a vo- luminous literature on aspect within linguistics and philosophy. Recently, computational linguists also have joined in the act within the context of machine translation or text understanding etc. For example, consider the following Japanese sentences (quoted from (Gunji, 1992)). (a). Ken-wa ima tonarino heya-de kimono-wo ki-te-i-ru. Ken-TOP now next room-LOC kimono-ACC put- on-PRES 'Ken is now putting on kimono in the next room.' (b). Ken-wa kesa-kara zutto axto kimono-wo ki-te-i-ru. Ken-TOP this morning-since always that kimono- ACC weax-PRES 'Ken has been wearing that kimono since this morn- ing.' (e). Ken-wa ano kimono-wo san-nen maeni ki-te-i-ru. Ken-TOP that kimono-ACC three-year before wear-PRES 'Ken has the experience of wearing that kimono three years ago.' Notice that English translations use separate lex- ical items (put on for (a) and wear for (b), (c)) and different aspectual configurations (the progres- sive for (a), the perfect progressive for (b), and an- other for (c)), while all Japanese sentences contain the same verbal form ki-te-i-ru. Thus. when the sys- tem tries to translate these sentences, it must be aware of the difference among them. This paper describes an approach to extract the aspectual information of Japanese verb phrases from a monolingual corpus. In the next section, we will classify Japanese verbs into six categories by means of aspectual features following the framework of (Bennett et al., 1990). The aspectual forms land adverbs are defined as the functions which operate on verbs' aspectual features and changes their val- ues. By using the constraints of the applicability of the functions, we can identify a unique category for each verb automatically. If one can acquire aspec- tual properties of verbs properly and know how the other constituents in a sentence operate on them, then the aspectual meaning of the whole sentence will be determined monotonically. To evaluate the result of the experiment, we will examine the mean- ing of -teiru which is one of the most fundamental aspectual forms, since the classification itself is …

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