LORENZO MARCONI

Dottore di ricerca

ciclo: XXXVI


supervisore: Riccardo Rosati

Titolo della tesi: Privacy-preserving and Inconsistency-tolerant Query Answering in Knowledge Bases and Databases

In recent decades, the widespread use of information systems has led to an increasing amount of the sensitive data managed, posing several privacy and security risks. Controlled Query Evaluation (CQE) is a framework for limiting access to sensitive information when querying a system, while still providing useful responses. Initially proposed for databases, CQE has recently been studied for Description Logics ontologies, the logical formalization underpinning most of Semantic Web technologies. Central to CQE is the possibility of specifying a data protection policy in a declarative way, avoiding the need to actively alter data to ensure their security. The policy is enforced via optimal censors, which aim to minimally alter information while maintaining confidentiality. Notably, censors satisfying the so-called indistinguishability property also ensure that the end user is not even able to discern if the answers to a query have been altered or not. The thesis investigates various CQE semantics based on the so-called optimal GA censors, which enjoy the indistinguishability property. In order not to arbitrarly pick a censor, we adopt the usual strategy of skeptical reasoning, i.e. answering according to all the optimal censors. Unfortunately, this approach is proven to be intractable, so we present an alternative semantics based on the intersection of all optimal GA censors (called IGA censor). Under this semantics, answering union of conjunctive queries (UCQs) in the Description Logic DL-LiteR is first-order (FO) rewritable, and thus in AC0 in data complexity. Anyway, the intersection-based approach may cause loosing too much information, which led us to explore smarter semantics for improving the throughput of query answers while preserving confidentiality. Towards this aim, we first show how to exploit a priority relation between ontology predicates for reducing the number of censors. Then, we consider the strategy of selecting censors in a dynamic way, exploiting the order in which queries are posed for maximizing the cooperativity of the system. In both cases, we provide suitable FO rewriting techniques, proving that the nice computational properties of the IGA semantics are preserved. The prioritized scenario also served as main setting for carrying out our experiments, wherein we implemented the newly-presented CQE techniques adapting them to the ontology-based data access methodology. Moreover, the research extends to the related field of Consistent Query Answering (CQA), which studies how to handle inconsistencies when answering queries. Specifically, we consider knowledge bases in which a set of existential rules must always be satisfied by the underlying database. A central notion in CQA is the one of repair, that is a maximal subset of the database satisfying all the rules. As for query answering, similarly as done in CQE, we examine both skeptical reasoning and the intersection-based semantics, known as AR and IAR, respectively. We study a very expressive language of rules and identify many subclasses where repair checking and UCQ entailment are tractable, or even FO rewritable. We finally investigate the integration between open and closed-world assumption, offering insights into utilizing open and closed predicates within the CQA framework, and provide the first set of complexity results for the aforenamed decision problems within this intriguing scenario.

Produzione scientifica

11573/1729517 - 2025 - Indistinguishability in controlled query evaluation over prioritized description logic ontologies
Cima, Gianluca; Lembo, Domenico; Marconi, Lorenzo; Rosati, Riccardo; Savo, Domenico Fabio - 01a Articolo in rivista
rivista: JOURNAL OF WEB SEMANTICS (Tokyo ; St. Louis ; San Diego ; Oxford ; New York ; London ; Amsterdam ; Philadelphia ; Shannon ; Paris ; Boston : Elsevier) pp. - - issn: 1570-8268 - wos: (0) - scopus: (0)

11573/1707667 - 2024 - A Gentle Introduction to Controlled Query Evaluation in DL-Lite Ontologies
Cima, Gianluca; Lembo, Domenico; Marconi, Lorenzo; Rosati, Riccardo; Savo, Domenico Fabio - 01a Articolo in rivista
rivista: SN COMPUTER SCIENCE (Singapore: Springer Nature) pp. - - issn: 2662-995X - wos: (0) - scopus: 2-s2.0-85189541441 (0)

11573/1717146 - 2024 - Enhancing Controlled Query Evaluation through Epistemic Policies
Cima, Gianluca; Lembo, Domenico; Marconi, Lorenzo; Rosati, Riccardo; Savo, Domenico Fabio - 04b Atto di convegno in volume
congresso: International Joint Conference on Artificial Intelligence (Jeju; South Korea)
libro: Proceedings of the Thirty-Third International Joint Conference on Artificial Intelligence (IJCAI-24) - (978-1-956792-04-1)

11573/1717169 - 2024 - Controlled Query Evaluation in DL-Lite through Epistemic Protection Policies (Extended Abstract)
Cima, Gianluca; Lembo, Domenico; Marconi, Lorenzo; Rosati, Riccardo; Savo, Domenico Fabio - 04d Abstract in atti di convegno
congresso: International Workshop on Description Logics (Bergen; Norway)
libro: Proceedings of the 37th International Workshop on Description Logics (DL 2024) - ()

11573/1687515 - 2023 - Dynamic Controlled Query Evaluation over DL-Lite Ontologies (Extended Abstract)
Bonatti, Piero; Cima, Gianluca; Lembo, Domenico; Marconi, Lorenzo; Rosati, Riccardo; Sauro, Luigi; Fabio Savo, Domenico - 04b Atto di convegno in volume
congresso: International Workshop on Description Logics (Rhodes; Greece)
libro: Proceedings of the 36th International Workshop on Description Logics (DL 2023) co-located with the 20th International Conference on Principles of Knowledge Representation and Reasoning and the 21st International Workshop on Non-Monotonic Reasoning (KR 2023 and NMR 2023) - ()

11573/1651064 - 2022 - Controlled Query Evaluation in OWL 2 QL: A "Longest Honeymoon" Approach
Bonatti, Piero; Cima, Gianluca; Lembo, Domenico; Marconi, Lorenzo; Rosati, Riccardo; Sauro, Luigi; Savo, Domenico Fabio - 04b Atto di convegno in volume
congresso: International Semantic Web Conference (Hangzhou; China)
libro: The Semantic Web – ISWC 2022 21st International Semantic Web Conference, Virtual Event, October 23–27, 2022, Proceedings - (978-3-031-19432-0)

11573/1571526 - 2021 - On Information Disclosure in Ontology-based Data Access (Extended Abstract)
Cima, Gianluca; Lembo, Domenico; Marconi, Lorenzo; Rosati, Riccardo; Fabio Savo, Domenico - 04b Atto di convegno in volume
congresso: 34th International Workshop on Description Logics (DL 2021) (Bratislava, Slovakia)
libro: Proceedings of the 34th International Workshop on Description Logics (DL 2021) part of Bratislava Knowledge September (BAKS 2021) - ()

11573/1571555 - 2021 - Controlled query evaluation over prioritized ontologies with expressive data protection policies
Cima, Gianluca; Lembo, Domenico; Marconi, Lorenzo; Rosati, Riccardo; Fabio Savo, Domenico - 04b Atto di convegno in volume
congresso: International Semantic Web Conference (Virtual Event)
libro: The Semantic Web – ISWC 2021 20th International Semantic Web Conference, ISWC 2021, Virtual Event, October 24–28, 2021, Proceedings - (9783030883607)

11573/1594479 - 2021 - Controlled Query Evaluation over Ontologies through Policies with Numerical Restrictions
Cima, Gianluca; Lembo, Domenico; Marconi, Lorenzo; Rosati, Riccardo; Savo, Domenico Fabio; Sinibaldi, Daniele - 04b Atto di convegno in volume
congresso: 4th Conference on Artificial Intelligence and Knowledge Engineering, AIKE 2021 (Virtual Event)
libro: 2021 IEEE Fourth International Conference on Artificial Intelligence and Knowledge Engineering (AIKE) - (978-1-6654-3736-3)

11573/1450653 - 2020 - Controlled Query Evaluation in Ontology-Based Data Access
Cima, Gianluca; Lembo, Domenico; Marconi, Lorenzo; Rosati, Riccardo; Savo, Domenico Fabio - 04b Atto di convegno in volume
congresso: International Semantic Web Conference (Athens; Greece)
libro: The Semantic Web – ISWC 2020 19th International Semantic Web Conference, Athens, Greece, November 2–6, 2020, Proceedings, Part I - (9783030624187)

© Università degli Studi di Roma "La Sapienza" - Piazzale Aldo Moro 5, 00185 Roma