Minimal Change and Maximal Coherence for Epistemic Logic Program Updates

We consider the problem of updating nonmonotonic knowledge bases represented by epistemic logic programs where disjunctive information and notions of knowledge and beliefs can be explicitly expressed. We propose a formulation for epistemic logic program updates based on a principle called minimal change and maximal coherence. The central feature of our approach is that during an update procedure, contradictory information is removed on a basis of minimal change under the semantics of epistemic logic programs and then coherent information is maximally retained in the update result. By using our approach, we can characterize an update result in both semantic and syntactic forms. We show that our approach handles update sequences and satisfies the consistency requirement. We also investigate important semantic properties of our update approach such as reduction, persistence and preservation.