tailieunhanh - Báo cáo khoa học: "TYPES IN FUNCTIONAL UNIFICATION GRAMMARS"

Functional Unification Grammars (FUGs) are popular for natural language applications because the formalism uses very few primitives and is uniform and expressive. In our work on text generation, we have found that it also has annoying limitations: it is not suited for the expression of simple, yet very common, taxonomic relations and it does not allow the specification of completeness conditions. We have implemented an extension of traditional functional unification. This extension addresses these limitations while preserving the desirable properties of FUGs. It is based on the notions of typed features and typed constituents. . | TYPES IN FUNCTIONAL UNIFICATION GRAMMARS Michael Elhadad Department of Computer Science Columbia University New York NY 10027 Internet Elhadad@ ABSTRACT Functional Unification Grammars FUGs are popular for natural language applications because the formalism uses very few primitives and is uniform and expressive. In our work on text generation we have found that it also has annoying limitations it is not suited for the expression of simple yet very common taxonomic relations and it does not allow the specification of completeness conditions. We have implemented an extension of traditional functional unification. This extension addresses these limitations while preserving the desừabỉe properties of FUGs. It is based on the notions of typed features and typed constituents. We show the advantages of this extension in the context of a grammar used for text generation. 1 INTRODUCTION . . Unification-based formalisms are increasingly used in linguistic theories Shieber 1986 and computational linguistics. In particular one type of unification formalism functional unification grammar FUG is widely used for text generation Kay 1979 McKeown 1985 Appelt 1985 Pairs 1987 McKeown Elhadad 1990 and is beginning to be used for parsing Kay 1985 Kasper 1987 . FUG enjoys such popularity mainly because it allies expressiveness with a simple economical formalism. It uses very few primitives has a clean semantics Pereira Shieber 1984 Kasper Rounds 1986 El-hadad 1990 is monotonic and grants equal status to function and structure in the descriptions. We have implemented a functional unifier El-hadad 1988 covering all the features described in Kay 1979 and McKeown Paris 1987 . Having used this implementation extensively we have found all these properties very useful but we also have met with limitations. The functional unification FU formalism is not well suited for the expression of simple yet very common taxonomic relations. The traditional way to implement such relations in