Extending SPARQL with regular expression patterns (for querying RDF)

RDF is a knowledge representation language dedicated to the annotation of resourceswithin the framework of the semantic web. Among the query languages for RDF, SPARQLallows querying RDF through graph patterns, i.e., RDF graphs involving variables. Otherlanguages, inspired by the work in databases, use regular expressions for searching pathsin RDF graphs. Each approach can express queries that are out of reach of the other one.Hence, we aim at combining these two approaches. For that purpose, we define a language,called PRDF (for “Path RDF”) which extends RDF such that the arcs of a graph can belabeled by regular expression patterns. We provide PRDF with a semantics extending thatof RDF, and propose a correct and complete algorithm which, by computing a particulargraph homomorphism, decides the consequence between an RDF graph and a PRDF graph.We then define the PSPARQL query language, extending SPARQL with PRDF graph pat-terns and complying with RDF model theoretic semantics. PRDF thus offers both graphpatterns and path expressions. We show that this extension does not increase the computa-tional complexity of SPARQL and, based on the proposed algorithm, we have implementeda correct and complete PSPARQL query engine.