A Feature-Based Constraint System for Logic Programming with Entailment

This paper presents the constraint system FT, which we feel is an intriguing alternative to Herbrand both theoretically and practically. As does Herbrand, FT provides a universal data structure based on trees. However, the trees of FT (called feature trees) are more general than the trees of Herbrand (called constructor trees), and the constraints of FT are ner grained and of diierent expressivity. The basic notion of FT are functional attributes called features, which provide for record-like descriptions of data avoiding the overspeciication intrinsic in Herbrand's constructor-based descriptions. The feature tree structure xes an algebraic semantics for FT. We will also establish a logical semantics, which is given by three axiom schemes xing the rst-order theory FT. FT is a constraint system for logic programming, providing a test for unsatissability, and a test for entailment between constraints, which is needed for advanced control mechanisms. The two major technical contributions of this paper are (1) an incremental entailment simpliication system that is proved to be sound and complete, and (2) a proof showing that FT satisses the so-called \independence of negative constraints".