A Proposal of Korean Conjugation System and its Application to Morphological Analysis

Language, Information and Computation(PACLIC 11),1996, 229-236 A Proposal of Korean Conjugation System and its Application to Morphological Analysis Yoshitaka Hirano� Yuji Matsumoto Nara Institute of Science and Technology Takayama, Ikoma, Nara 630-01 Japan {yosita-h,matsu}Ois.aist-nara.ac.jp Abstract This paper presents a new Korean verb conjugation system, which enables an easy treatment of Korean morphological phenomena such as contraction. This makes the size of the dictionary for ending forms to be small. We also introduce a Korean morphological analysis system. Korean morphological analysis system generally analyzes sentences within the segments(a part between spaces). We propose a system that considers the information beyond segmentation. 1 Introduction Korean has many irregular transformation such as contraction. Korean mor- phological analysis system MoA treats contraction within its system (J.-H.Kim 1994). We propose a method to treat such phenomena by means of a verb conjugation system. Korean verbs generally have many ending forms in con- jugation. For example, 7}c}.(go) has 7F as its stem, and takes a variety of conjugated endings such as id L. , 7 1 ad, L and so on. In this way each verb requires a distinct set of ending forms. When we connect the ending eat..1 zF with a verb, 7 FU 1- becomes 11-LI (stem:7F + ending: H LI-CO but 1:c1-(eat) becomes g4 OL1 El- (stem: 124 + ending: trLI 1-). The ending LILF takes the form id LI El- or ;ILI LF according to the verb. The. conjugated form of the ending depends on the verb to which it is connected. When we compile a dictionary, we have to include all possible words with possible endings. However, this method is not practical. We propose a method in which all surface variations are explained by verb conjugation. For example, as for the nonconjugational ending H Li*, the verb 7I-CF conjugates to 71- and the verb CF conjugates to Then, 7F CI- becomes 7,:ftirl- (stem:7F + conjugational ending:none + nonconjugational ending: td LIEF), and� becomes� r F (stem: + conjugational ending: + nonconjugational ending: H LI CF). After proposing a verb conjugation system, we describe a Korean mor- phological analysis system as a direct application of it. 229 In Korean morphological analysis, methods to reduce ambiguities have been studied. However, most of the systems analyze sentences only within segments (Eojeol, i.e., a sequence of morphemes surrounded by spaces)(J.- H.Kim 1995). We propose a method to reduce some ambiguities by means of using an information over segment boundary. 2 Verb conjugation We prepare 24 conjugation types and seven conjugation forms for each of them. The conjugation types consists of five vowel stem verbs, two regular consonant stem verbs and nineteen irregular verbs. All verbs are classified into 24 types. Table 1 shows seven conjugation forms and Table 2 shows some exam- ples of verb conjugation. Table 3 shows a list of vowel stern verbs and their suffix vowels. In Table 2, '+' indicates a positive vowel stem verb and indicates a negative vowel stem verb. 'reg' means a regular conjugation verb, and 'irg' means …

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