Belief Change: Partial Epistemic Priorities and Logical Non-Omniscience

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  • Technical report TR92-09. In many database applications, designers can easily provide at least some information about the relative importance of the information to be stored and manipulated. While of potentially high value, the ordering information is typically only partial. Here we address the issue of updates in such partially ordered situations, which we call epistemically stratified databases. In the current database theory literature, Alchourron, Gardenfors and Makinson (AGM) have proposed a collection of rationality postulates that define rational updates to deductively closed databases. We reformulate the AGM framework to accomodate empistemically stratified databases, and to relax the closure requirement. Our immediate goal is to exploit the use of partial ordering information and to relax the logical omniscient flavour of the closure condition. A more ambitious goal is only hinted at; it is motivated by a desire to develop a more general theory of updates that integrates the naturally related ideas in artificial intelligence and deductive databases. Our approach begins with the definition of a new contraction operator which uses the information provided by the partial order to make a rational choice amongst the various possible outcomes of the update operation. This operator is shown to satisfy a reformulated set of rationality requirements. A second and similar contraction operator based on a logically omniscient framework is shown to satisfy most of the original AGM rationality postulates for contraction. | TRID-ID TR92-09

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    Attribution 3.0 International