In Ontology-Based Data Access (OBDA), a domain ontology is linked to the data sources of an organization in order to query, integrate and manage data through the concepts and relations of the domain of interest, thus abstracting from the structure and the implementation details of the data layer. While the great majority of contributions in OBDA in the last decade have been concerned with the issue of computing the answers of queries expressed over the ontology, recent papers address a different problem, namely the one of providing suitable abstractions of data services, i.e., characterizing or explaining the semantics of queries over the sources in terms of queries over the domain ontology. Current works on this subject are based on expressing abstractions in terms of unions of conjunctive queries (UCQs). In this paper we advocate the use of a non-monotonic language for this task. As a first contribution, we present a simple extension of UCQs with nonmonotonic features, and show that non-monotonicity provides more expressive power in characterizing the semantics of data services. A second contribution is to prove that, similarly to the case of monotonic abstractions, depending on the expressive power of the languages used to specify the various components of the OBDA system, there are cases where neither perfect nor approximated abstractions exist for a given data service. As a third contribution, we single out interesting special cases where the existence of abstractions is guaranteed, and we present algorithms for computing such abstractions in these cases.

Non-Monotonic Ontology-based Abstractions of Data Services / Cima, Gianluca; Lenzerini, Maurizio; Poggi, Antonella. - (2020), pp. 243-252. (Intervento presentato al convegno KR 2020 - the 17th International Conference on Principles of Knowledge Representation and Reasoning tenutosi a Virtual Conference; Worldwide) [10.24963/kr.2020/25].

Non-Monotonic Ontology-based Abstractions of Data Services

Gianluca Cima
;
Maurizio Lenzerini
;
Antonella Poggi
2020

Abstract

In Ontology-Based Data Access (OBDA), a domain ontology is linked to the data sources of an organization in order to query, integrate and manage data through the concepts and relations of the domain of interest, thus abstracting from the structure and the implementation details of the data layer. While the great majority of contributions in OBDA in the last decade have been concerned with the issue of computing the answers of queries expressed over the ontology, recent papers address a different problem, namely the one of providing suitable abstractions of data services, i.e., characterizing or explaining the semantics of queries over the sources in terms of queries over the domain ontology. Current works on this subject are based on expressing abstractions in terms of unions of conjunctive queries (UCQs). In this paper we advocate the use of a non-monotonic language for this task. As a first contribution, we present a simple extension of UCQs with nonmonotonic features, and show that non-monotonicity provides more expressive power in characterizing the semantics of data services. A second contribution is to prove that, similarly to the case of monotonic abstractions, depending on the expressive power of the languages used to specify the various components of the OBDA system, there are cases where neither perfect nor approximated abstractions exist for a given data service. As a third contribution, we single out interesting special cases where the existence of abstractions is guaranteed, and we present algorithms for computing such abstractions in these cases.
2020
KR 2020 - the 17th International Conference on Principles of Knowledge Representation and Reasoning
Source-to-Ontology Rewriting; Ontology-based Data Access; Description Logics; Conjunctive Query; Epistemic Logic; Computational Complexity
04 Pubblicazione in atti di convegno::04b Atto di convegno in volume
Non-Monotonic Ontology-based Abstractions of Data Services / Cima, Gianluca; Lenzerini, Maurizio; Poggi, Antonella. - (2020), pp. 243-252. (Intervento presentato al convegno KR 2020 - the 17th International Conference on Principles of Knowledge Representation and Reasoning tenutosi a Virtual Conference; Worldwide) [10.24963/kr.2020/25].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11573/1457971
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