Actions that make you change your mind : belief revision in an agent-oriented setting

Abstract

In this paper we study the dynamics of belief from an agent-oriented, semantics-based point of view. In a formal framework used to specify and to reason about formal agents, we dene actions that model three well- known changes of belief, viz. expansions, contractions, and revisions. We treat these belief changes as full- edged actions by dening both the op- portunity for and result of these actions, and the ability of agents to apply these belief-changing actions. In dening the result of the contraction ac- tion we introduce the concept of selection functions. These are special functions that select a subset of the set of states that is to be added to the set of doxastic alternatives of an agent, thereby contracting its set of beliefs. The action that models belief revisions is dened as the sequen- tial composition of a contraction and an expansion. We show that these belief-changing actions are dened in an intuitively acceptable, reasonable way by proving that the G?ardenfors postulates for belief changes are val- idated. The ability of agents to apply belief-changing actions is dened in terms of their knowledge and belief. These denitions are such that actions that an agent is capable of performing lead to desired states of aairs. The resulting framework provides an intuitively acceptable yet simple formalization of expansions, contractions and revisions as actions in a dynamic/epistemic, agent-oriented framework.