Composition in Hierarchical CLP

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 noncompositional. We define a scheme for composing together solutions to individual hierarchies and show that hierarchy composition can be expressed very simply using filtering functions over bags (multisets); we present some properties of these functions, and define and explain an alternative to bag intersection which is also used in our scheme. We present an example involving three strength levels and show that we can achieve a close approximation to the solutions produced by standard HCLP.