Controlled Query Evaluation over Ontologies through Policies with Numerical Restrictions

We study Controlled Query Evaluation (CQE), a declarative approach to privacy-preserving query answering. In particular, we focus on the application of CQE to ontologies and analyze the possibility of using role cardinality restrictions in the formulas expressing a data protection policy. We start from an existing framework for CQE over DL-Lite ontologies, and extend the policy language of the existing framework defining a class of formulas (called numerical restriction axioms) with role number restrictions. We show that the computational properties of the existing framework are not affected by the extension of the policy language. In particular, conjunctive query answering over DL-Lite(H,horn) ontologies under the CQE semantics (IGA) is still FO-rewritable and is in AC0 with respect to data complexity.