tailieunhanh - Báo cáo khoa học: "Inference in DATR"

DATR is a declarative language for representing a restricted class of inheritance networks, permitting both multiple and default inheritance. The principal intended area of application is the representation of lexical entries for natural language processing, and we use examples from this domain throughout. In this paper we present the syntax and inference mechanisms for the language. The goal of the DATR enterprise is the design of a simple language that (i) has the necessary expressive power to encode the lexical entries presupposed by contemporary work in the unification grammar tradition, (ii) can express all the evident generalizations about such. | Inference in DATR Roger Evans Gerald Gazdar School of Cognitive and Computing Sciences University of Sussex BRIGHTON BN1 9QN Abstract DATR is a declarative language for representing a restricted class of inheritance networks permitting both multiple and default inheritance. The principal intended area of application is the representation of lexical entries for natural language processing and we use examples from this domain throughout. In this paper we present the syntax and inference mechanisms for the language. The goal of the DATR enterprise is the design of a staple language that i has the necessary expressive power to encode the lexical entries presupposed by contemporary work in the unification grammar ttadition ii can express all the evident generalizations about such entries iii has an explicit theory of inference iv is computationally tractable and v has an explicit declarative semantics. The present paper is primarily concerned with iii though the examples used may hint at our strategy in respect of i and ii . 1 Introduction Inheritance networks semantic nets provide an intuitively appealing way of thinking about the representation of various kinds of knowledge. This fact has not gone unnoticed by a number of researchers woiking on lexical knowledge representation . de Smedt 1984 Flickinger et al. 1985 Calder te Lindert 1987 Daelemans 1987a 1987b Gazdar 1987 and Calder 1989 . However many such networks have been realized in the context of programming systems or programming languages that leave their precise meaning unclear. In the light of Brachman 1985 Ether-ington 1988 and much other recent work it ha become apparent that the formal properties 01 notations intended to represent inheritance an highly problematic. Although not discussec here DATR has a formal semantics Evans Gazdar 1989 for which some completeness anc soundness results have been derived. These results and others on complexity for example will be provided in a subsequent paper. Then are