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Abstract : |
Abstract. Feature Constraint Systems have been proposed as a logical data structure for constraint (logic) programming. They provide a record-like view to trees by identifying subtrees by keyword rather than by position. Their atomic constraints are finer grained than in the constructor-based approach. The recently proposed CFT [15] in fact generalizes the rational tree system of Prolog II. We propose a new feature constraint system EF which extends CFT by considering features as first class values. As a consequence, EF contains constraints like x[v]w where v is a variable ranging over features, while CFT restricts v to be a fixed feature symbol. We show that the satisfiability of conjunctions of atomic EF-constraints is NP-complete. Satisfiability of quantifier-free EF-constraints is shown to be decidable, while the 9, |
