Giorgio Stefanoni

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In order to meet usability requirements, most logic-based applications provide explanation facilities for reasoning services. This holds also for Description Logics, where research has focused on the explanation of both TBox reasoning and, more recently, query answering. Besides explaining the presence of a tuple in a query answer, it is important to(More)
So-called combined approaches answer a conjunctive query over a description logic ontology in three steps: first, they materialise certain consequences of the ontology and the data; second, they evaluate the query over the data; and third, they filter the result of the second phase to eliminate unsound answers. Such approaches were developed for various(More)
OWL 2 EL is a popular ontology language that supports role inclusions—axioms of the form S1 · · ·Sn v S that capture compositional properties of roles. Role inclusions closely correspond to context-free grammars, which was used to show that answering conjunctive queries (CQs) over OWL 2 EL knowledge bases with unrestricted role inclusions is undecidable.(More)
Answering conjunctive queries (CQs) over EL knowledge bases (KBs) with complex role inclusions is PSPACE-hard and in PSPACE in certain cases; however, if complex role inclusions are restricted to role transitivity, a tight upper complexity bound has so far been unknown. Furthermore, the existing algorithms cannot handle reflexive roles, and they are not(More)
In order to meet usability requirements, most logic-based applications provide explanation facilities for reasoning services. This holds also for DLs, where research has focused on the explanation of both TBox reasoning and, more recently, query answering. Besides explaining the presence of a tuple in a query answer, it is important to explain also why a(More)
In order to meet usability requirements, most logic-based applications provide explanation facilities for reasoning services. This holds also for DLs, where research focused on the explanation of both TBox reasoning and, more recently, query answering. Besides explaining the presence of a tuple in a query answer, it is important to explain also why a given(More)
In a double blind, controlled clinical study, 40 patients, 20 of whom were subjected to mastectomy or quadrantectomy and 20 to inguinal hernioplasty, were randomly assigned to two treatment groups of 20 subjects each, balanced by type of operation. Treatment lasted 3 days and involved the administration of 3 suppositories per day of nimesulide or diclofenac(More)
Biological scientists have made large amounts of data available on the Web, which can be accessed by canned or precomputed queries presented via web forms. To satisfy further information needs, users currently have to have a good understanding of SQL and how the data is stored in the database. While accessing information at the ontological layer seems more(More)
Description Logics are a key technology in data management scenarios such as Ontology-Based Data Access (OBDA), a paradigm in which a DL ontology is used to provide a conceptual view of the data [1]. An OBDA system transforms a conjunctive query over the ontology into a query over the data sources [2]. This transformation is independent of the data, so the(More)
Combined approaches have become a successful technique for CQ answering over ontologies. Existing algorithms, however, are restricted to the logics underpinning the OWL 2 profiles. Our goal is to make combined approaches applicable to a wider range of ontologies. We focus on RSA: a class of Horn ontologies that extends the profiles while ensuring(More)