Detection of Japanese Homophone Errors by a Decision List Including a Written Word as a Default Evidence

Proceedings of EACL '99 Detection of Japanese Homophone Errors by a Decision List Including a Written Word as a Default Evidence Hiroyuki Shinnou Ibaraki University Dept. of Systems Engineering 4-12-1 Nakanarusawa Hitachi, Ibaraki, 316-8511, JAPAN shinnou@lily, dse. ibaraki, ac. jp Abstract In this paper, we propose a practical method to detect Japanese homophone errors in Japanese texts. It is very important to detect homophone errors in Japanese revision systems because Japanese texts suffer from homophone errors frequently. In order to detect ho- mophone errors, we have only to solve the homophone problem. We can use the decision list to do it because the homo- phone problem is equivalent to the word sense disambiguation problem. However, the homophone problem is different from the word sense disambiguation problem because the former can use the written word but the latter cannot. In this pa- per, we incorporate the written word into the original decision list by obtaining the identifying strength of the written word. The improved decision list can raise the F-measure of error detection. 1 Introduction In this paper, we propose a method of detect- ing Japanese homophone errors in Japanese texts. Our method is based on a decision list proposed by Yarowsky (Yarowsky, 1994; Yarowsky, 1995). We improve the original decision list by using writ- ten words in the default evidence. The improved decision list can raise the F-measure of error de- tection. Most Japanese texts are written using Japanese word processors. To input a word composed of kanji characters, we first input the phonetic hira- gana sequence for the word, and then convert it to the desired kanji sequence. However, multiple converted kanji sequences are generally produced, and we must then choose the correct kanji se- quence. Therefore, Japanese texts suffer from ho- mophone errors caused by incorrect choices. Care- lessness of choice alone is not the cause of homo- phone errors; Ignorance of the difference among homophone words is serious. For example, many Japanese are not aware of the difference between '.~.,'~,' and '~,~,', or between '~.~.' and ,~,t. In this paper, we define the term homophone set as a set of words consisting of kanji charac- ters that have the same phone 2. Then, we define the term homophone word as a word in a ho- mophone set. For example, the set { ~/~-~ (proba- bility), ~7 (establishment)} is a homophone set because words in the set axe composed of kanji characters that have the same phone 'ka-ku-ri-tu'. Thus, q/~' and '~f_' are homophone words. In this paper, we name the problem of choosing the correct word from the homophone set the homo- phone problem. In order to detect homophone errors, we make a list of homophone sets in ad- vance, find a homophone word in the text, and then solve the homophone problem for the homo- phone word. Many methods of solving the homophone prob- lem have been proposed (Tochinai et al., 1986; Ibuki et al., 1997; Oku and Matsuoka, 1997; Oku, 1994; Wakita and Kaneko, 1996). …

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