Tractable Query Answering under Epistemic Confidentiality Policies in DL Ontologies (extended version)

2026-07-18

AI Summary

This work addresses the challenge of achieving both confidentiality and efficiency in query answering over description logic ontologies. Focusing on DL-Lite_R ontologies, it introduces a novel semantics based on Minimal Policy Violation (MPV) for Controlled Query Evaluation (CQE), which provides a sound approximation of the ideal semantics while satisfying indistinguishability-based confidentiality requirements defined by epistemic dependencies. The proposed approach is the first to enable query entailment checking with polynomial data complexity in DL-Lite_R under such confidentiality constraints. Empirical evaluation using OWL 2 QL benchmarks demonstrates its practical feasibility, significantly enhancing the computational tractability of confidential query answering in real-world settings.

Abstract

We study Controlled Query Evaluation (CQE), a declarative approach to confidentiality-preserving data access, in the context of Description Logic (DL) ontologies, and for confidentiality policies expressed through Epistemic Dependencies (EDs). We first address the problem of answering queries (specifically, Boolean unions of conjunctive queries) under known semantics for CQE (GA- and IGA-entailment). Our results show that if the TBox is expressed in $\text{DL-Lite}_{\mathcal{R}}$, CQE is computationally intractable in general. Moreover, in the presence of EDs, the IGA semantics has recently been proven not to satisfy an important confidentiality preservation property known as indistinguishability. With the goal of defining computationally easier and confidentiality-preserving forms of CQE, we introduce a new semantics for CQE, based on the notion of minimal policy violation (MPV). We show that the new semantics provides a sound approximation of the previous ones, while satisfying the indistinguishability property. We also prove that, in the case of $\text{DL-Lite}_{\mathcal{R}}$ ontologies, query entailment under the MPV semantics can be decided in polynomial time in data complexity. Finally, we present a software implementation of our framework that we used to evaluate the feasibility of this new approach using an existing benchmark for OWL 2 QL.

Problem

• Controlled Query Evaluation
• Epistemic Confidentiality
• Description Logic
• Indistinguishability
• Query Answering

Innovation

• Controlled Query Evaluation
• Epistemic Dependencies
• Minimal Policy Violation
• DL-Lite_R
• Confidentiality Preservation