A compositional theory of constraint hierarchies (Operational semantics)

Abstract

We propose a variant of the Hierarchical Constraint Logic Programming (HCLP) scheme of Borning, Wilson, and others. We consider compositionality and incrementality in Constraint Logic Programming, introduce HCLP, and present Wilson's proof that it is non-compositional. We define a scheme which uses bags (multisets) called BCH (Bags for the Composition of Hierarchies) for composing together solutions to individual hierarchies; it calculates a superset of the solutions expected from HCLP. We prove that BCH is compositional. We then define FGH (Filters, Guards, Hierarchies), a non-compositional scheme which removes precisely those BCH solutions which are unacceptable to HCLP. Thus we separate HCLP into two parts, one compositional and one non-compositional.