Querying the Semantic Web with RQL

Real scale Semantic Web applications such as Knowledge Portals and E Marketplaces require the management of voluminous repositories of resource metadata The Resource Description Framework RDF enables the creation and exchange of metadata as any other Web data Although large volumes of RDF descriptions are already appearing su ciently expressive declarative query languages for RDF are still missing We propose RQL a new query language adapting the functionality of semistructured or XML query languages to the peculiarities of RDF but also extending this functionality in order to uniformly query both RDF descriptions and schemas RQL s a typed language following a functional approach a la OQL and relies on formal graph model that permits the interpretation of superimposed resource descriptions created using one or more RDF schemas We illustrate the syntax semantics and type system of RQL and report on the performance of RSSDB our persistent RDF Store for storing and querying voluminous RDF metadata