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Lorenzo Marconi

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4 papers

1 author row

IJCAI Conference 2025 Conference Paper

Assessing the Exposure to Public Knowledge in Policy-Protected Description Logic Ontologies

Gianluca Cima
Domenico Lembo
Lorenzo Marconi
Riccardo Rosati
Domenico Fabio Savo

We propose a general framework for assessing the exposure of sensitive knowledge in policy-protected knowledge bases (KBs), where knowledge is represented as logical theories and data protection policies are defined declaratively using epistemic dependencies. The framework models scenarios in which confidential parts of the KB may be publicly known due to security breaches. We study two fundamental decision problems: determining whether the exposed knowledge violates the data protection policy (leakage), and whether there exists a secure view of the KB that complies with the policy. We analyze the computational complexity (specifically, data complexity) of these problems, focusing on the DL-Lite_R and EL_\bot Description Logics. Our findings show that, for DL-Lite_R with restricted forms of policy, both the problems can be efficiently solved through query rewriting methods. For EL_\bot, we establish conditions for tractable computational bounds. Our results highlight the potential of this framework for practical applications in confidentiality-preserving knowledge management.

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AAAI Conference 2025 Conference Paper

Consistent Query Answering over Existential Rules with Open and Closed Predicates

Lorenzo Marconi
Riccardo Rosati

We study Consistent Query Answering (CQA) over knowledge bases with existential rules. Specifically, we propose a novel framework for CQA that combines previous approaches, allowing for the simultaneous presence of both open and closed predicates, i.e. predicates interpreted under open- and closed-world assumption, respectively. We establish the data complexity of answering unions of conjunctive queries in such a new framework under the so-called AR semantics and for different classes of existential rules. We also provide new complexity results for the standard (i.e. non-inconsistency tolerant) query answering in the presence of both open and closed predicates. Our results show that, for certain classes of rules, the complexity of CQA matches that of non-inconsistency-tolerant query answering.

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AIJ Journal 2025 Journal Article

Enhancing cooperativity in controlled query evaluation over ontologies

Piero Bonatti
Gianluca Cima
Domenico Lembo
Francesco Magliocca
Lorenzo Marconi
Riccardo Rosati
Luigi Sauro
Domenico Fabio Savo

Controlled Query Evaluation (CQE) is a methodology designed to maintain confidentiality by either rejecting specific queries or adjusting responses to safeguard sensitive information. In this investigation, our focus centers on CQE within Description Logic ontologies, aiming to ensure that queries are answered truthfully as long as possible before resorting to deceptive responses, a cooperativity property which is called the “longest honeymoon”. Our work introduces new semantics for CQE, denoted as MC-CQE, which enjoys the longest honeymoon property and outperforms previous methodologies in terms of cooperativity. We study the complexity of query answering in this new framework for ontologies expressed in the Description Logic DL-Lite_R. Specifically, we establish data complexity results under different maximally cooperative semantics and for different classes of queries. Our results identify both tractable and intractable cases. In particular, we show that the evaluation of Boolean unions of conjunctive queries is the same under all the above semantics and its data complexity is in AC^0. This result makes query answering amenable to SQL query rewriting. However, this favorable property does not extend to open queries, even with a restricted query language limited to conjunctions of atoms. While, in general, answering open queries in the MC-CQE framework is intractable, we identify a sub-family of semantics under which answering full conjunctive queries is tractable.

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IJCAI Conference 2024 Conference Paper

Enhancing Controlled Query Evaluation through Epistemic Policies

Gianluca Cima
Domenico Lembo
Lorenzo Marconi
Riccardo Rosati
Domenico Fabio Savo

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-LiteR. 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.

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