Abstract
Policy-based inference control of queries submitted to a logic-oriented information system aims at confining answers to queries such that the user cannot infer the validity of any sentence specified in a confidentiality policy. Such a control requires us to consider the history of queries and answers to a particular user. In most previous approaches, the control system captures the history by maintaining a fictitious view the user is supposed to generate by exploiting rational reasoning. In this paper, we propose and explore an alternative option to represent the history, namely by suitably adapting the confidentiality policy after returning an answer to a query. Basically, such a policy adaptation precomputes all relevant steps of formal proofs that the fictitious view logically implies some policy element. Focusing on propositional information systems, we present a comprehensive protocol for policy adaptation, which always keeps the current version of the confidentiality policy redundancy-free and fully vulnerable. This protocol is formally proved to be effective by a reduction argument, showing that policy adaptation is able to simulate the achievements of maintaining a view. We also briefly discuss the efficiency for special cases under dedicated data structures.