Compiling Prioritized Default Rules into Ordinary Logic Programs

by Benjamin N. Grosof

Abstract: We give a new approach to the semantics and implementation of prioritized default rules: to compile them into ordinary logic programs (with forward or backward inferencing, not simply Prolog). We use the compilation approach both to expressively generalize and to implement courteous logic programs (LP's), a previous formalism featuring classical negation and prioritized conflict handling. We show that we preserve courteous LP's' attractive reasoning behaviors and polynomial-time computational cost. Our expressive generalization enables recursion, and also reasoning about the prioritization. Our implementation enables courteous LP's functionality to be added modularly to ordinary LP rule engines, via a pre-processor, with moderate, tractable computational overhead. More generally, we show that the compilation approach is applicable to implementing, and to defining, numerous variants of prioritized default rule KR's, beyond the particular courteous LP variant given here.

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