Controlled Query Evaluation through Epistemic Dependencies

TL;DR

This paper introduces a novel approach to Controlled Query Evaluation using epistemic dependencies, enabling richer data protection policies and providing a tractable solution for acyclic cases, advancing confidentiality-preserving query answering.

Contribution

It presents a new policy language based on epistemic dependencies for CQE, demonstrating its expressive power and providing a practical query rewriting algorithm for acyclic dependencies.

Findings

The policy language significantly extends existing CQE approaches.

CQE with epistemic dependencies is generally intractable, but tractable for acyclic dependencies.

A query rewriting algorithm is proposed for acyclic epistemic dependencies.

Abstract

In this paper, we propose the use of epistemic dependencies to express data protection policies in Controlled Query Evaluation (CQE), which is a form of confidentiality-preserving query answering over ontologies and databases. The resulting policy language goes significantly beyond those proposed in the literature on CQE so far, allowing for very rich and practically interesting forms of data protection rules. We show the expressive abilities of our framework and study the data complexity of CQE for (unions of) conjunctive queries when ontologies are specified in the Description Logic DL-Lite_R. Interestingly, while we show that the problem is in general intractable, we prove tractability for the case of acyclic epistemic dependencies by providing a suitable query rewriting algorithm. The latter result paves the way towards the implementation and practical application of this new approach to CQE.