Distance Semantics for Belief Revision

1 I n t r o d u c t i o n Intelligent agents must gather information about the world, elaborate theories about it and revise those theories in view of new information that , sometimes, contradicts the beliefs previously held. Belief revision is therefore a central topic in Knowledge Representation. It has been studied in different forms: numeric or symbolic, procedural or declarative, logical or probabilistic. One of the most successful framework in which belief revision has been studied has been proposed by Alchourr6n, G£rdenfors and *This work was partially supported by the Jean and Helene Alfassa fund for research in Artificial Intelligence and by grant 136/94-1 of the Israel Science Foundation on "New Perspectives on Nonmonotonic Reasoning". tUniversit~ de Provence, 3, Place Victor Hugo, F-13331 Marseille C~dex 3, France, [email protected],fr $Institute of Computer Science, Hebrew University, 91904 Jerusalem, Israel, [email protected] §Institute of Mathematics, Hebrew University, 91904 Jerusalem, Israel, [email protected],huji.ac.il