A Paper Abstract by Benjamin Grosof

Generalizing Prioritization (April 28 1991)

by Benjamin N. Grosof

Abstract: We identify several bases for prioritization information. This motivates us to generalize the idea of prioritization that was introduced, in the context of circumscription, by John McCarthy (1986) and formalized by Vladimir Lifschitz (1985). We show that the structure of the prioritization partial order (i.e., the partial order over the set of minimized predicates) was previously restricted in such a way ("layered" or "stratified") as to be unsuitable for many applications of default reasoning, including inheritance. We overcome this by showing how to generalize the prioritization partial order to be any well-founded (e.g., finite) strict partial order. We show how to prioritize arbitrary model-preference criteria, and their syntactic correspondents. One application of this is to generalize prioritized circumscription. We also develop the concept of composing prioritization and show how to prioritize preference criteria expressing internally-prioritized groups of minimized predicates (or defaults). We show that this enables one to express hierarchical modularity in the specification of default reasoning. Our definition of prioritization subsumes, as special cases, several previous ideas about precedence in the non-monotonic reasoning literature. It is applicable to any kind of preference criteria, even those not about models, as long as they obey the properties of reflexivity and transitivity.
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