DFG-Graduiertenkolleg Mathematische Logik und Anwendungen

Graduiertenkolloquium SS 2008

Vorträge

• 28.04.2008
  Herr Dr. Andrea Calì
  Taming the infinite chase: query answering under expressive relational constraints Abstract
  

• 23.06.2008, Zeit: 9:00 Uhr - 13:00 Uhr, Ort: 02-016, Georges-Köhler-Allee 101
  Tutorial über Ontology-based Data Access Summary
  Der Vortragende, Herr Prof. Diego Calvanese (calvanese "AT" inf.unibz.it), kommt von der Free University of Bozen-Bolzano.

Taming the infinite chase: query answering under expressive relational constraints
An important task in Knowledge Representation is answering queries posed over a knowledge base, represented as a set of facts plus a set of rules. In this talk we address the problem of answering conjunctive queries posed over knowledge bases where rules are an extension of logic programming rules, that may have existentially quantified variables in the head; this kind of rules are traditionally called tuple-generating dependencies (TGDs) in the database literature, but they are broadly used in Description Logics and in ontological reasoning. In this setting, the chase is an important tool for query answering; so far, most of the research has concentrated on cases where the chase terminates. We define and study large classes of TGDs under which the query evaluation problems remain decidable even in case the chase does not terminate; we provide tight complexity bounds for such cases. Our results immediately extend to query containment.

Tutorial über Ontology-based Data Access
Many organizations nowadays face the problem of accessing existing data sources by means of mechanisms that are sufficiently expressive without compromising efficiency. Ontologies allow one to describe the domain of interest of an information system at a high level of abstraction, and are widely considered as a suitable formal tool for sophisticated data access.
In this tutorial we provide a comprehensive understanding of the problem of ontology-based data access, both from the theoretical and from the practical points of view. We address several problems that are crucial in this context:

• the /trade-off/ between the /expressive power/ of the ontology language and the /efficiency/ of computing answers to queries;
• the /processing of queries/ posed over the ontology by accessing the data stored in the sources;
• the /impedance mismatch/ between the abstract objects at the ontology level and the concrete data values stored in data sources;
• the /integration/ of multiple data sources;
• the mutual /inconsistency/ of data and constraints in the ontology.