Querying Semistructured (Meta)Data and Schemas on the Web: The case of RDF RDFS

The need for descriptive information, i.e., metadata, about Web resources has been recognized in several application contexts (e.g., digital libraries, infomediaries, portals, etc.). The Resource Description Framework (RDF) aims at facilitating the creation and exchange of metadata, as any other Web data. In particular, the de nition of schema vocabularies enables the interpretation of RDF descriptions across several communities. Unfortunately, existing RDF-enabled systems (e.g., browsers, search engines) totally ignore RDF schemas. In this paper, we propose RQL, a declarative language suitable for querying both RDF descriptions and schemas. RQL relies on a graph data model capturing the RDF modeling primitives in terms of classes and relationship types, organized into appropriate subsumption taxonomies. Furthermore, a graph instantiation mechanism is introduced to interpret semistructured RDF data using schema information. Taxonomies of labels are then exploited transparently in order to facilitate querying of complex semistructured data as well as of the schema vocabularies themselves. To the best of our knowledge RQL is the rst language o ering this functionality.