Semantic Web Query Languages

DEFINITION A number of formalisms have been proposed for representing data and meta data on the Semantic Web. In particular, RDF, Topic Maps and OWL allow one to describe relationships between data items, such as concept hierarchies and relations between the concepts. A key requirement for the Semantic Web is integrated access to data represented in any of these formalisms, as well the ability to also access data in the formalisms of the “standard Web”, such as (X)HTML and XML. This data access is the objective of Semantic Web query languages. A wide range of query languages for the Semantic Web exist, ranging from i) pure “selection languages” with only limited expressivity, to fully-fledged reasoning languages, and ii) from query languages restricted to a certain data representation format, such as XML or RDF, to general purpose languages that support multiple data representation formats and allow simultaneous querying of data on both the standard and Semantic Web.