Dipartimento di Ingegneria informatica, automatica e gestionale

Controlled Query Evaluation (CQE) is a confidentiality-preserving framework in which private information is protected through a policy, and a (optimal) censor guarantees that answers to queries are maximized without violating the policy. CQE has been recently studied in the context of ontologies, where the focus has been mainly on the problem of the existence of an optimal censor. In this paper we instead study query answering over all possible optimal censors. We establish data complexity of this problem for ontologies specified in the Description Logics DL-LiteR and EL⊥ and for variants of the censor language, which is the language used by the censor to enforce the policy. In our investigation we also analyze the relationship between CQE and the problem of Consistent Query Answering (CQA). Some of the complexity results we provide are indeed proved through mutual reduction between CQE and CQA.