Representing Belief Revision through Default Theories

João C. P. da SilvaSheila R. M. Veloso

We examine the representations of epistemic states and their revision processes (RP) through default theories (DTs). Using a sphere-based semantics for DTs we characterize a RP as a sequence of consistent expansions without using contractions. We show that DTs provide an unifying framework for revision in both semantical and syntactical-based approaches as well as in coherent and foundation approaches. Motivated by Nebel's work, we propose to extend the use of default theories in two directions: (i) using supernormal default theories to represent semantical classified revision processes; (ii) using general default theories and some variants of Reiter's default logics to represent foundation classified revision processes. We define revision operators, which can be viewed as a revision on the epistemic states, represented by a DT T, by a sentence. Basically, they are defined via some operations on the class of the extensions of a default theory T' obtained from T and .

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