D1.4.4 Reasoning over Distributed Networked Ontologies and Data Sources

The concept of the semantic web is based on the ability to reason over explicitly declared or defined knowledge, so as to infer new, implicit knowledge in a sound way. The ontology, as a shared specification of a conceptualization, provides the basic tool for explicitly authoring this specified knowledge. Towards this direction, the World Wide Web Consortium has already endorsed the Web Ontology Language (OWL). OWL consists of a family of languages, diversified along their expressiveness and decidability. It is based on different fragments of Description Logics, a powerful fragment of First Order Predicate Calculus, which allows for knowledge description in a formal and well-understood way. On the other hand, the reasoning component has been primarily served by the theoretical results on description logics and as a result efficient reasoners have been proposed and implemented. Theoretical research and practical implementations so far have usually focused on the centralized reasoning paradigm. Under this paradigm, one can assume the existence of one global ontology, defining a number of concepts and their relationships as well, and of a reasoner that executes a reasoning algorithm on the ontology and produces the inferred knowledge. Such a model, however, does not mirror the aspirations of the Semantic Web. Indeed, we argue that more has to be done, since large-scales are an indispensable part of the semantic web vision. In the current Deliverable we aim at investigating the distributed aspects of knowledge representation formalisms and the reasoning procedures they are equipped with. Moreover, we propose three novel approaches that deal with the problems of 1) efficient reasoning in distributed knowledge bases, 2) reasoning with integrated distributed description logics, and 3) reasoning with (distributed) temporarily unavailable data sources, respectively.