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Báo cáo khoa học: "Packing of Feature Structures for Efficient Unification of Disjunctive Feature Structures"

This paper proposes a method for packing feature structures, which automatically collapses equivalent parts of lexical/phrasal feature structures of HPSG into a single packed feature structure. This method avoids redundant repetition of unification of those parts. Preliminary experiments show that this method can significantly improve a unification speed in parsing. | Packing of Feature Structures for Efficient Unification of Disjunctive Feature Structures Yusuke Miyao Department of Information Science University of Tokyo 7-3-1 Kongo Bunkyo-ku Tokyo 113-0033 Japan E-mail yusukeQis. s. u-tokyo .ac.jp Abstract This paper proposes a method for packing feature structures which automatically collapses equivalent parts of lexical phrasal feature structures of HPSG into a single packed feature structure. This method avoids redundant repetition of unification of those parts. Preliminary experiments show that this method can significantly improve a unification speed in parsing. 1 Introduction Efficient treatment of syntactic semantic ambiguity is a key to making efficient parsers for wide-coverage grammars. In feature-structurebased grammars1 such as HPSG Pollard and Sag 1994 ambiguity is expressed not only by manually-tailored disjunctive feature structures but also by enumerating non-disjunctive feature structures. In addition there is ambiguity caused by non-determinism when applying lexical grammar rules. As a result a large number of lexical phrasal feature structures are required to express ambiguous syntactic semantic structures. Without efficient processing of these feature structures a sufficient parsing speed is unattainable. This paper proposes a method for packing feature structures which is an automatic optimization method for parsers based on feature structure unification. This method automatically extracts equivalent parts of feature structures and collapses them into a single packed feature structure. A packed feature structure can be processed more efficiently because we can avoid redundant repetition of unification of the equivalent parts of original feature structures. There have been many studies on efficient In this paper we consider typed feature structures described in Carpenter 1992 . unification of disjunctive feature structures Kasper and Rounds 1986 Hasida 1986 Dôrre and Eisele 1990 Nakano 1991 Blache 1997 .