SQUALL: The expressiveness of SPARQL 1.1 made available as a controlled natural language

The Semantic Web (SW) is now made of billions of triples, which are available as Linked Open Data (LOD) or as RDF stores. The SPARQL query language provides a very expressive way to search and explore this wealth of semantic data. However, user-friendly interfaces are needed to bridge the gap between end-users and SW formalisms. Navigation-based interfaces and natural language interfaces require no or little training, but they cover a small fragment of SPARQL's expressivity. We propose SQUALL, a query and update language that provides the full expressiveness of SPARQL 1.1 through a flexible controlled natural language (e.g., solution modifiers through superlatives, relational algebra through coordinations, filters through comparatives). A comprehensive and modular definition is given as a Montague grammar, and an evaluation of naturalness is done on the QALD challenge. SQUALL is conceived as a component of natural language interfaces, to be combined with lexicons, guided input, and contextual disambiguation. It is available as a Web service that translates SQUALL sentences to SPARQL, and submits them to SPARQL endpoints (e.g., DBpedia), therefore ensuring SW compliance, and leveraging the efficiency of SPARQL engines.