Terp: Syntax for OWL-friendly SPARQL Queries

Web Ontology Language (OWL) [5] can be seen as an extension of Resource Description Framework (RDF). The primary exchange syntax for OWL is RDF/XML, and every OWL ontology can be represented as an RDF graph. But there is no standard query language specifically for OWL ontologies. The most commonly used Semantic Web query language is SPARQL [7], which is intended to be used for RDF. Roughly speaking, SPARQL is specified as queries matching RDF graphs with simple RDF entailment. However, it allows this definition to be extended to OWL entailment. A semantics for SPARQL compatible with OWL DL has been defined in SPARQL-DL [8] and a similar formalization of OWL-compatible SPARQL semantics is being developed by the W3C’s SPARQL Working Group as part of SPARQL 1.1. The semantics extension of SPARQL allows one to query OWL ontologies and get the expected results with respect to OWL entailments. However, writing SPARQL queries that involve complex OWL expressions ranges from challenging to unpleasant because SPARQL query syntax is based on Turtle [1], which isn’t intended for OWL. SPARQL queries against OWL data have to encode the RDF serialization of OWL expressions: these queries are typically verbose, difficult to write, and difficult to understand. In this paper we present Terp, a new syntax that combines Turtle and Manchester syntaxes to provide maximum legibility and conciseness when querying OWL with SPARQL. More precisely, Terp syntax allows class, property, and data range expressions, expressed in Manchester syntax, to be used inside SPARQL queries. In this paper, we provide examples to demonstrate how Terp reuses existing features from well-known syntaxes to make SPARQL queries of OWL data more concise and more legible.