tailieunhanh - Báo cáo khoa học: "Encoding Lexicalized Tree Adjoining Grammars with a Nonmonotonic Inheritance Hierarchy"

This paper shows how DATR, a widely used formal language for lexical knowledge representation, can be used to define an I_TAG lexicon as an inheritance hierarchy with internal lexical rules. A bottom-up featural encoding is used for LTAG trees and this allows lexical rules to be implemented as covariation constraints within feature structures. Such an approach eliminates the considerable redundancy otherwise associated with an LTAG lexicon. | Encoding Lexicalized Tree Adjoining Grammars with a Nonmonotonic Inheritance Hierarchy Roger Evans Information Technology Research Institute University of Brighton Gerald Gazdar School of Cognitive Computing Sciences University of Sussex David Weir School of Cognitive Computing Sciences University of Sussex Abstract This paper shows how DATR a widely used formal language for lexical knowledge representation can be used to define an LTAG lexicon as an inheritance hierarchy with internal lexical rules. A bottom-up featu-ral encoding is used for LTAG trees and this allows lexical rules to be implemented as covariation constraints within feature structures. Such an approach eliminates the considerable redundancy otherwise associated with an LTAG lexicon. 1 Introduction The Tree Adjoining Grammar TAG formalism was first introduced two decades ago Joshi et al. 1975 and since then there has been a steady stream of theoretical work using the formalism. But it is only more recently that grammars of non-trivial size have been developed Abeille Bishop Cote Schabes 1990 describe a feature-based Lexicalized Tree Adjoining Grammar LTAG for English which subsequently became the basis for the grammar used in the XTAG system a wide-coverage LTAG parser Doran et al. 1994b Doran et al. 1994a XTAG Research Group 1995 . The advent of such large grammars gives rise to questions of efficient representation and the fully lexicalized character of the LTAG formalism suggests that recent research into lexical representation might be a place to look for answers see for example Briscoe ei al. 1993 Daelemans Gazdar 1992 . In this paper we explore this suggestion by showing how the lexical knowledge representation language lkrl DATR Evans ẲỈ Gazdar 1989a Evans Gazdar 1989b can be used to formulate a compact hierarchical encoding of an LTAG. The issue of efficient representation for LTAG1 is discussed by Vijay-Shanker Schabes 1992