tailieunhanh - Báo cáo khoa học: "Multiple Default Inheritance in a Unification-Based"

A formalism is presented for lexical specification in unification-based grammars which exploits defeasible multiple inheritance to express regularity, subregularity, and exceptions in classifying the properties of words. Such systems are in the general case intractable; the present proposal represents an attempt to reduce complexity while retaining sufficient expressive power for the task at hand. Illustrative examples are given of morphological analyses from English and German. | Multiple Default Inheritance in a Unification-Based Lexicon Graham Russell John Carroll Susan Warwick-Armstrong ISSCO 54 route des Acacias 1227 Geneva Switzerland Abstract A formalism is presented for lexical specification in unification-based grammars which exploits defeasible multiple inheritance to express regularity subregularity and exceptions in classifying the properties of words. Such systems are in the general case intractable the present proposal represents an attempt to reduce complexity while retaining sufficient expressive power for the task at hand. Illustrative examples are given of morphological analyses from English and German. 1 Introduction The primary task of a computational lexicon is to associate character strings representing word forms with information able to constrain the distribution of those word forms within a The organization of a lexicon requires the ability on the one hand to make general statements about classes of words and on the other to express exceptions to such statements affecting individual words and subclasses of words. These considerations have provoked interest in applying to the lexicon Al knowledge representation techniques involving the notions of inheritance and The sys current address Cambridge University Computer Laboratory New Museums Site Pembroke Street Cambridge CB2 3QG UK. We are indebted to Afzal Ballim Mark Johnson and anonymous referees for valuable comments on this paper. In the general case the relation between forms and information is many-to-many rather than one-to-many as often assumed and this observation has influenced the choice of facilities incorporated within the system. See below for an example of how distinct forms share identical mor. phosyntactic specifications. 3See . Daelemans and Gazdar eds. 1990 and the references in Gazdar 1990 . The work of Hudson 1984 extends this general approach to sentence syntax. tern described heie is put of the ELU3