Towards Data-Integration on the Semantic Web: Querying RDF with Xcerpt

Although RDF is serialized using XML, the many possible syntactic forms and the need for inferencing make it difficult to query RDF using existing XML query languages. Numerous new query languages for RDF with built-in knowledge about the semantics of particular inferencing formalisms like RDF Schema and OWL have been proposed or are currently under development. However most, if not all, are specific to RDF and not capable of querying arbitrary XML data. In order to better integrate and leverage both kinds of data on the Semantic Web, a new generation of versatile Web query languages is needed, allowing uniform querying and integration of both the traditional Web and the emerging new content of the Semantic Web. This thesis investigates querying RDF using Xcerpt, a declarative, rule-based query and transformation language for XML and other semi-structured data on the Web. Two representations of RDF data as Xcerpt data terms are proposed, realized as views over concrete serializations of RDF data in arbitrary XML-based serialization formats. Furthermore, the possibility of implementing RDF Schema inferencing directly using Xcerpt rules is investigated. Finally, this thesis examines several use cases, demonstrating the advantages of a query language that can query and integrate the traditional Web and the Semantic Web.