AAAI Publications, Sixteenth International Conference on Principles of Knowledge Representation and Reasoning

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Specifying Plausibility Levels for Iterated Belief Change in the Situation Calculus
Toryn Q. Klassen, Sheila A. McIlraith, Hector J. Levesque

Last modified: 2018-09-24


We investigate augmenting a theory of belief and actions with qualitative plausibility levels. Shapiro et al. created a framework for modeling iterated belief revision and update which integrated those features with the well-developed theory of action in the situation calculus. However, applying their technique requires associating plausibility levels with initial situations, for which no very convenient mechanism had been proposed. Schwering and Lakemeyer proposed deriving these initial plausibility levels from a set of conditionals, similarly to how models are ranked in Pearl's System Z. However, their approach inherits some limitations of System Z. We consider alternatives, and argue that a perspicuous approach is to measure plausibility by counting the abnormalities in a situation (similarly to cardinality-based circumscription). By allowing abnormalities to change over time, we can also model changing plausibility levels in a natural and simple way, which gives us a flexible approach for handling belief change about predicted and unpredicted exogenous actions.


situation calculus; only-knowing; cardinality-based circumscription; plausibility

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