RDF and XML: Towards a Unified Query Layer

One of the requirements of current Semantic Web applications is to deal with heterogeneous data. The Resource Description Framework (RDF) is the W3C recommended standard for data representation, yet data represented and stored using the Extensible Markup Language (XML) is almost ubiquitous and remains the standard for data exchange. While RDF has a standard XML representation, XML Query languages are of limited use for transformations between natively stored RDF data and XML. Being able to work with both XML and RDF data using a common framework would be a great advantage and eliminate unnecessary intermediate steps that are currently used when handling both formats. 1 XML and RDF transformations In many application domains combining and converting between XML and RDF data is a useful but often not trivial task, relying mostly on XSLT, or – more recently – XQuery. The importance of this issue is acknowledged within the W3C, for instance the Gleaning Resource Descriptions from Dialects of Languages (GRDDL) [6] and Semantic Annotations for WSDL (SAWSDL) [8] recommendations stress the problem of lifting arbitrary XML formats to RDF and vice versa (lowering). The W3C GRDDL working group has the goal to complement the concrete RDF/XML syntax with a mechanism to relate it to other XML dialects (especially XHTML o