Abstract
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 consider query answering
over all possible optimal censors. We study 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 obtained
through mutual reduction between CQE and CQA