On the revision of preferences and rational inference processes

Orderings and inference relations can be successfully used to model the behavior of a rational agent. This behavior is indeed represented either by a set of ordered pairs that reflect the agent's preferences, or by a rational inference relation that describes the agent's internal logics. In the finite case where we work, both structures admit a simple representation by means of logical chains. The problem of revising such inference processes arises when it appears necessary to modify the original model in order to take into account new facts about the agent's behavior. How is it then possible to perform the desired modification? We study here the possibilities offered by the technique of ‘chain revision’ which appears to be the easiest way to treat this kind of problem: the revision is performed through a simple modification of the logical chain attached to the agent's behavior, and the revision problem boils down to adding, retracting or modifying some of the links of the original chain. This perspective permits an effective treatment of the problems of both simple and multiple revision. The technique developed can also be used in some limiting cases, when the agent's inference process is only partially known, encoded by an incomplete set of preferences or a conditional knowledge base.