tailieunhanh - Báo cáo khoa học: "INCORPORATING INHERITANCE AND FEATURE STRUCTURES INTO A LOGIC GRAMMAR FORMALISM"

The result, which we call Inheritance G r a m m a r , is a proper superset of DCG and includes many features of PATR-II. Its taxonomic reasoning facilitates semantic type-class represent lexical, syntactic and semantic categories and other feature values. In many formalisms (. DCG and PATR-II), equality is the only operation for symbols; in IG symbols are related in an IS-A hierarchy. | INCORPORATING INHERITANCE AND FEATURE STRUCTURES INTO A LOGIC GRAMMAR FORMALISM Harry H. Porter III Oregon Graduate Center 19600 . Von Neumann Dr. Beaverton Oregon 97006-1999 ABSTRACT Hassan Ait-Kaci introduced the ự -term an informational structure resembling featurebased functional structures but which also includes taxonomic inheritance Ait-Kaci 1984 . We describe ựí-terms and how they have been incorporated into the Logic Grammar formalism. The result which we call Inheritance Grammar is a proper superset of DCG and includes many features of PATR-II. Its taxonomic reasoning facilitates semantic type-class reasoning during grammatical analysis. INTRODUCTION The Inheritance Grammar IG formalism is an extension of Hassan Ait-Kaci s work on terms Ait-Kaci 1984 Ait-Kaci and Nasr 1986 . A 0-term is an informational structure similar to both the feature structure of PATR-II Shieber 1985 Shieber et al 1986 and the first-order term of logic. v -terms are ordered by subsumption and form a lattice in which unification of 0-terms amounts to greatest lower bounds GLB n . In Inheritance Grammar 0-terms are incorporated into a computational paradigm similar to the Definite Clause Grammar DCG formalism Pereira and Warren 1980 . Unlike feature structures and first-order terms the atomic symbols of v -terms are ordered in an IS-A taxonomy a distinction that is useful in performing semantic type-class reasoning during grammatical analysis. We begin by discussing this ordering. THE IS-A RELATION AMONG FEATURE VALUES Like other grammar formalisms using feature-based functional structures we will assume a fixed set of symbols called the signature. These symbols are atomic values used to represent lexical syntactic and semantic categories and other feature values. In many formalisms . DCG and PATR-n equality is the only operation for symbols in IG symbols are related in an IS-A hierarchy. These relationships are indicated in the grammar using statements such as1 boy .