Base Revision Operations and Schemes : Semantics , Representation

The theory of belief revision developed by GG ar-denfors and his colleagues characterizes the classes of reasonable belief revision operations. However, some of the assumptions made in the theory of belief revision are unrealistic from a computational point of view. We address this problem by considering revision operations that are based on a priority ordering over a set of sentences representing a belief state instead of using preference relations over all sentences that are accepted in a belief state. In addition to providing a semantic justiication for such operations, we investigate also the computational complexity. We show how to generate an epistemic entrenchment ordering for a belief state from an arbitrary priority ordering over a set of sentences representing the belief state and show that the resulting revision is very eecient. Finally, we show that some schemes for generating revision operations from bases can encode the preference relations more concisely than others.