CQE in OWL 2 QL: A "Longest Honeymoon" Approach (extended version)

TL;DR

This paper introduces a dynamic Controlled Query Evaluation method for OWL 2 QL ontologies that adapts answers based on query history to maximize data protection and cooperation, with first-order rewritability ensuring practical applicability.

Contribution

It proposes a novel dynamic CQE approach that considers query history, unlike static methods, and demonstrates first-order rewritability for OWL 2 QL with denials, enabling practical algorithms.

Findings

Dynamic CQE adapts answers based on previous queries.

The approach maximizes answer availability while protecting confidentiality.

Query evaluation remains first-order rewritable, ensuring efficiency.

Abstract

Controlled Query Evaluation (CQE) has been recently studied in the context of Semantic Web ontologies. The goal of CQE is concealing some query answers so as to prevent external users from inferring confidential information. In general, there exist multiple, mutually incomparable ways of concealing answers, and previous CQE approaches choose in advance which answers are visible and which are not. In this paper, instead, we study a dynamic CQE method, namely, we propose to alter the answer to the current query based on the evaluation of previous ones. We aim at a system that, besides being able to protect confidential data, is maximally cooperative, which intuitively means that it answers affirmatively to as many queries as possible; it achieves this goal by delaying answer modifications as much as possible. We also show that the behavior we get cannot be intensionally simulated through a static approach, independent of query history. Interestingly, for OWL 2 QL ontologies and policy expressed through denials, query evaluation under our semantics is first-order rewritable, and thus in AC0 in data complexity. This paves the way for the development of practical algorithms, which we also preliminarily discuss in the paper.