tailieunhanh - Báo cáo khoa học: "An Algebra for Semantic Construction in Constraint-based Grammars"

We develop a framework for formalizing semantic construction within grammars expressed in typed feature structure logics, including HPSG. The approach provides an alternative to the lambda calculus; it maintains much of the desirable flexibility of unificationbased approaches to composition, while constraining the allowable operations in order to capture basic generalizations and improve maintainability. | An Algebra for Semantic Construction in Constraint-based Grammars Ann Copestake Computer Laboratory University of Cambridge New Museums Site Pembroke St Cambridge UK aac@ Alex Lascarides Division of Informatics University of Edinburgh 2 Buccleuch Place Edinburgh Scotland UK alex@ Dan Flickinger CSLI Stanford University and YY Software Ventura Hall 220 Panama St Stanford CA 94305 USA danf@ Abstract We develop a framework for formalizing semantic construction within grammars expressed in typed feature structure logics including HPSG. The approach provides an alternative to the lambda calculus it maintains much of the desirable flexibility of unificationbased approaches to composition while constraining the allowable operations in order to capture basic generalizations and improve maintainability. 1 Introduction Some constraint-based grammar formalisms incorporate both syntactic and semantic representations within the same structure. For instance Figure 1 shows representations of typed feature structures TFSs for Kim sleeps and the phrase Kim sleeps in an HPSG-like representation loosely based on Sag and Wasow 1999 . The semantic representation expressed is intended to be equiv-alentto x Kim A sleep e x .1 Note 1. Variable equivalence is represented by coindexation within a TF S. 2. The coindexation in Kim sleeps is achieved as an effect of instantiating the SUBJ slot in the sign for sleeps. 3. Structures representing individual predicate applications henceforth elementary predications or EPs are accumulated by an append operation. Conjunction of EPs is implicit. 1 The variables are free we will discuss scopal relationships and quantifiers below. 4. All signs have an index functioning somewhat like a A-variable. A similar approach has been used in a large number of implemented grammars see Shieber 1986 for a fairly early example . It is in many ways easier to work with than A-calculus based approaches which we .