A Logic-Based Implementation of Head-Driven Phrase Structure Grammar

Head-Driven Phrase Structure Grammar (HPSG), a unification-based formal language for describing linguistic phenomena, has a declarative semantics which makes it amenable to specification as a logic program. The HPSG formalism has undergone significant modification, becoming more declarative and incorporating greater lexicalization, since Proudian and Pollard first introduced a LISP-based HPSG chart parser in 1985. These theoretical developments have led us to the Prolog implementation of an HPSG interpreter which is described in this paper. We provide a brief introduction to the HPSG formalism, and then illustrate how a natural language grammar based on this formalism can be stated in a declarative notation that is directly interpretable by a Prolog chart-parser. This process leads us to refinements in both the specification of the formalism and the interpretation methodology.