Iterated Belief Change |
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Authors: | Aditya K Ghose Pablo O Hadjinian Abdul Sattar Jia-H You Randy Goebel |
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Affiliation: | University of Alberta, Edmonton, Canada, and University of Wollongong, Australia;, University of Alberta, Edmonton, Canada;, Griffith University, Nathan, Brisbane, Australia |
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Abstract: | Most existing formalizations treat belief change as a single-step process, and ignore several problems that become important when a theory, or belief state, is revised over several steps. This paper identifies these problems, and argues for the need to retain all of the multiple possible outcomes of a belief change step, and for a framework in which the effects of a belief change step persist as long as is consistently possible. To demonstrate that such a formalization is indeed possible, we develop a framework, which uses the language of PJ-default logic (Delgrande and Jackson 1991) to represent a belief state, and which enables the effects of a belief change step to persist by propagating belief constraints . Belief change in this framework maps one belief state to another, where each belief state is a collection of theories given by the set of extensions of the PJ-default theory representing that belief state. Belief constraints do not need to be separately recorded; they are encoded as clearly identifiable components of a PJ-default theory. The framework meets the requirements for iterated belief change that we identify and satisfies most of the AGM postulates (Alchourrón, Gärdenfors, and Makinson 1985) as well. |
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Keywords: | knowledge representation belief revision nonmonotonic reasoning |
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