Dynamic Programming Method for Analyzing Conjunctive Structures in Japanese

Dynamic Programming Method for Analyzing Conjunctive Structures in Japanese Sadao Kurohashi and Makoto Nagao Dept. of Electrical Engineering, Kyoto University Yoshida-honmachi, Sakyo, Kyoto, 606, Japan kuro@kuee.kyoto-u.ac.jp Abstract Parsing a long sentence is very difficult, since long sentences often have conjunctions which result in am- biguities. If the conjunctive structures existing in a long sentence can be analyzed correctly, ambiguities can be reduced greatly and a sentence can be parsed in a high successful rate. Since the prior part and the posterior part of a conjunctive structure have a similar structure very often, finding two similar series of words is an essential point in solving this problem. Similarities of all pairs of words are calculated and then the two series of words which have the great- est sum of similarities are found by a technique of dynamic programming. We deal with not only con- junctive noun phrases, but also conjunctive predica- tive clauses created by "Renyoh chuushi-ho". We will illustrate the effectiveness of this method by the anal- ysis of 180 long Japanese sentences. 1 Introduction Analysis of a long Japanese sentence is one of many difficult problems which cannot be solved by the con- tinuing efforts of many researchers and remain abau- doned. It is difficult to get a proper analysis of a sentence whose length is more than fifty Japanese characters, and almost all the analyses fail for sen- tences composed of more than eighty characters. To clarify why it is is also very difficult because there are varieties of reasons for the failures. People some- times say that there are so many possibilities of modi- fier/modifyee relations between phrases in a long sen- tence. But no deeper consideration has ever been given for the reasons of the analysis failure. Analysis failure here means not only that no correct analysis is included in the multiple analysis results which are caused by the intrinsic ambiguity of a sentence and also by inaccurate grammatical rules, but also that the analysis fails in the middle of the analysis pro- re88, We have been claiming that many (more than two) linguistic components are to be seen at the same time in a sentence for proper parsing, and also that tree to tree transformation is necessary for reliable analysis of a sentence. Popular grammar rules which merge two linguistic components into one are quite insuf- ficient to describe the delicate relationships among components ill a long sentence. Language is complex. There often happens that components whicb are far apart in a long sentence co- occur, or have certain relationships. Such relations may be sometimes purely semantic, but often they are grammatical or structural, although they are not definite but very subtle. A long sentence, particularly of Japanese, con- tains parallel structures very often. They are ei- ther conjunctive noun phrases, or conjunctive pred- icative clauses. The latter is called "Renyoh chuushi- ho". They appear in an embedded sentence to mod- ify nouns, and also are used to connect two or more sentences. This form …

Content truncated to 500 words