Classification of Modality Function and Its Application to Japanese Language Analysis

CLASSIFICATION OF MODALITY FUNCTION AND ITS APPLICATION TO JAPANESE LANGUAGE ANALYSIS Shozo NArro, Akira SHIMAZU, and Hirosato NOMURA Musashino Electrical Communication Laboratories, N.T.T. 3-9-11, Midori-cho, Musashino-shi, Tokyo, 180, Japan Abstract This paper proposes an analysis method for Japanese modality. In this purpose, meaning of Japanese modality is classified into four semantic categories and the role of it is formalized into five modality functions. Based on these formalizations, information and constraints to be applied to the modality analysis procedure are specified. Then by combining these investigations with case analysis, the analysis method is proposed. This analysis method has been applied to Japanese analysis for machine translation. 1. Introduction Since the meaning of a sentence consists of both proposition and rnodality, TM analysis of modality is as indispensable as that of proposition for natural language understanding and machine translation. However studies on natural language analysis have mainly concerned with the propositional part, and algorithms for analyzing rnodality have not yet been sufficiently developed. The aim of this paper is to clarify the function of modality and to propose a method for analyzing the modality in Japanese sentences. Structure of a Japanese complex sentence can be formalized roughly by iterative concatenation of simple sentences. The simple sentence consists of cases and a predicate. The cases have surface representations of noun phrases or adverb phrases while the predicate has that of verb or adjective or adjective verb. A noun phrase is defined as the recursive concatenation of noun phrase or that of embedded sentence. We have employed '.he case structure as a basic meaning structure for a simple sentence, and extended it to retain the construction of complex sentences mentioned. Modaiity is additive information represented by auxiliary words such as modal particles, ending particles, and auxiliary verbs and sentence adverbs. The modal particle is attached to a noun phrase or a sentence element while the ending particle is attached to the enci position of a sentence. The auxiliary verb !mmediately follows a verb phrase. Modality represented in such grammatically different context is incorporated into the case structure, and the result construction is named as an extended case structure Ivl which enable us to propose a uniform framework for analyzing both proposition and modality. In this paper, we first classify modality into four semantic categories. Second, we define five modality functions using the logical representation of the meaning and then characterize the roles of each function. Third, we specify hard problems to be resolved in modality analysis. Fourth, we list the information and constraints to be considered in establishing the procedure of modality analysis. Then, we propose a method for analyzing modality based on these investigations. Finally, we exemplify the analysis by showing translations from Japanese into English. The method has been used to analyze Japanese sentences in a machine translation system. 17~ 2, Classification of modality Traditionally, modality has been classified into three categories, i.e. tense, aspect and modal. :0-! This classification is not sufficient for the deep analysis of the meaning structure of …

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