Department of Computer, Control and Management Engineering

In Controlled Query Evaluation (CQE) confidential data are protected through a declarative policy and a (optimal) censor, which guarantees that answers to queries are maximized without disclosing secrets. In this paper we consider CQE over Description Logic ontologies and study query answering over all optimal censors. We establish data complexity of the problem for ontologies specified in DL-LiteR 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.