Tassos Venetis

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Query rewriting over lightweight ontologies, like DL-Lite ontologies, is a prominent approach for ontology-based data access. It is often the case in realistic scenarios that users ask an initial query which they later refine, e.g., by extending it with new constraints making their initial request more precise. So far, all DL-Lite systems would need to(More)
— The Semantic Web can be viewed as largely about " Knowledge meets the Web ". Thus its vision includes ontologies and rules. A key requirement for the architecture of the Semantic Web is to be able to layer " rules on top of ontologies " and " ontologies on top of rules ". This has as a counterpart the definition of a mapping between Description Logics and(More)
Interoperability is a strong requirement in open distributed systems and in the Semantic Web. The need for ontology integration is not always completely met by the available ontology matching techniques because, in most cases, the semantics of the compared ontologies is not considered, thus leading to inconsistent mappings. Probabilistic approaches has been(More)
Conjunctive query answering is a key reasoning service for many ontology-based applications. With the advent of lightweight on-tology languages, such as OWL 2 QL, several query answering systems have been proposed which compute the so called UCQ rewriting of a given query. It is often the case in realistic scenarios, that users refine their original(More)
Computing a (Union of Conjunctive Queries - UCQ) rewriting R for an input query and ontology and evaluating it over the given dataset is a prominent approach to query answering over ontologies. However, R can be large and complex in structure hence additional techniques, like query subsumption and data constraints, need to be employed in order to minimise(More)
Ontologies expressed in Description Logics or extensions of Datalog are gradually used for describing the domain of many research and industrial strength applications. They provide a formal semantically rich and data-independent layer over which user queries can be posed. A prominent technique for query answering in ontology-based applications is query(More)
Fuzzy extensions to Description Logics (DLs) have gained considerable attention the last decade. So far most works on fuzzy DLs have focused on either very expressive languages, like fuzzy OWL and OWL 2, or on highly inexpressive ones, like fuzzy OWL 2 QL and fuzzy OWL 2 EL. To the best of our knowledge a fuzzy extension to the language OWL 2 RL has not(More)