tailieunhanh - Báo cáo khoa học: "Representing a System of Lexical Types Using Default Unification"

Default inheritance is a useful tool for encoding linguistic generalisations that have exceptions. In this paper we show how the use of an order independent typed default unification operation can provide non-redundant highly structured and concise representation to specify a network of lexical types, that encodes linguistic information about verbal subcategorisation. The system of lexical types is based on the one proposed by Pollard and Sag (1987), but uses the more expressive typed default feature structures, is more succinct, and able to express linguistic sub-regularities more elegantly. . | Proceedings of EACL 99 Representing a System of Lexical Types Using Default Unification Aline Villavicencio Computer Laboratory University of Cambridge New Museums Site Pembroke Street Cambridge CB2 3QG England Abstract Default inheritance is a useful tool for encoding linguistic generalisations that have exceptions. In this paper we show how the use of an order independent typed default unification operation can provide non-redundant highly structured and concise representation to specify a network of lexical types that encodes linguistic information about verbal subcategorisation. The system of lexical types is based on the one proposed by Pollard and Sag 1987 but uses the more expressive typed default feature structures is more succinct and able to express linguistic sub-regularities more elegantly. 1 Introduction Several authors have highlighted the importance of using defaults in the representation of linguistic knowledge in order to get linguistically adequate descriptions for some natural language phenomena Gazdar 1987 Bouma 1992 Daelemans et al 1992 Briscoe 1993 . Defaults have been used in the definition of inflectional morphology specification of lexical semantics analysis of gapping constructions and ellipsis among others. In this paper we use defaults to structure the lexicon concentrating on the description of verbal subcategorisation information. The issue of how to organise lexical information is especially important when a lexicalised formalism like Categorial Grammar CG or Head-Driven Phrase Structure Grammar HPSG is employed since the burden of linguistic description is concentrated in the lexicon and if lexical entries are organised as unrelated lists there is a significant loss of generalisation and an increase in redundancy. Alternatively it is possible to use inheritance networks which provide representations that are able to capture linguistic regularities about classes of items that behave similarly. This .