tailieunhanh - Báo cáo khoa học: "Conditional Descriptions in Functional Unification Grammar"

A grammatical description often applies to a linguistic object only when that object has certain features. Such conditional descriptions can be indirectly modeled in Kay's Functional Unification Grammar (FUG) using functional descriptions that are embedded within disjunctive alternatives. An extension to FUG is proposed that allows for a direct representation of conditional descriptions. This extension has been used to model the input conditions on the systems of systemic grammar. Conditional descriptions are formally defined in terms of logical implication and negation. This formal definition enables the use of conditional descriptions as a general notational extension to any of the. | Conditional Descriptions in Functional Unification Grammar Robert T. Kasper USC Information Sciences Institute 4676 Admiralty Way Suite 1001 Marina del Rey CA 90292 . Abstract A grammatical description often applies to a linguistic object only when that object has certain features. Such conditional descriptions can be indirectly modeled in Kay s Functional Unification Grammar FUG using functional descriptions that are embedded within disjunctive alternatives. An extension to FUG is proposed that allows for a direct representation of conditional descriptions. This extension has been used to model the input conditions on the systems of systemic grammar. Conditional descriptions are formally defined in terms of logical implication and negation. This formal definition enables the use of conditional descriptions as a general notational extension to any of the unification-based grammar representation systems currently used in computational linguistics. 1 Introduction Functional Unification Grammar Kay79 FUG and other grammatical formalisms that use feature structures and unification provide a general basis for the declarative representation of natural language grammars. In order to utilize some of the computational tools available with unification grammars we have developed a mapping from eyatemic gramman Hall76 into FUG notation. This mapping has been used as the first step in creating a general parsing method for systemic grammars Kas87a . The experience of translating systemic grammars into FUG has shown several ways in which the notational resources of FUG may be improved. In particular FUG has limited notational resources for expressing conditional information. In this paper we describe how FUG has been enhanced by the addition of conditional descriptions building on research that has already been reported Kas87a Kas86 Kas87b . Conditional information is stated explicitly in systemic grammars by the input conditions of systems that specify when a system must be