A fully denotational semantics for model-preference default systems

Propositional systems of default inference based on the dyadic relation of "preference" between models have recently been proposed by Selman and Kautz to provide a computationally tractable mechanism for the generation of vivid knowledge bases. In this paper we argue that the formalism proposed, albeit retaining a strong semantic flavour, may not be considered a full-fledged model-theoretic semantics, as no ontology which is independent of the existence of the knowledge representation language is postulated. Consistently with good model-theoretic practice we carry on to postulate a language-independent ontology and to use it in the subsequent definition of a fully denotational semantics for model-preference default systems.