SPARQL rewriting for query mediation over mapped ontologies

Περίληψη: In the recent years establishing interoperability and supporting data integration has become a major research challenge for the web of data. Uniform information access of heterogeneous sources is of major importance for Semantic Web applications and end users. We describe a methodology for SPARQL query mediation over federated OWL/RDF knowledge bases. The query mediation exploits mappings between semantically related entities of the mediator ontology (global ontology) and the federated site ontologies (local ontologies). A very rich set of mapping types, based on Description Logic semantics, is supported. The SPARQL queries which are posed over the global ontology are decomposed, rewritten, and then submitted to the federated sources. The rewritten SPARQL queries are locally evaluated and the results are returned to the mediator. We describe the formal modeling of executable mappings (i.e. mappings that can be used in SPARQL query rewriting), as well as the theoretic and implementation aspects of SPARQL query rewriting. Finally, we describe the implementation of a system supporting the mediation process