A Mapping of SPARQL Onto Conventional SQL

Abstract. This paper documents a semantics for expressing relational data as an RDF graph [RDF] and an algebra for mapping SPARQL SELECT queries over that RDF to SQL queries over the original relational data. The RDF graph, called the stem graph, is constructed from the relational structure and a URI identifier called a stem URI. The algebra specifies a function taking a stem URI, a relational schema and a SPARQL query over the corresponding stem graph, and emitting a relational query, which, when executed over the relational data, produces the same solutions at the SPARQL query executed over the stem graph. Relational databases exposed on the Semantic Web can be queried with SPARQL with the same performance as with SQL