On the Semantics of R2RML and its Relationship with the Direct Mapping

The W3C Relational Database to RDF (RDB2RDF) standards are positioned to bridge the gap between Relational Databases and the Semantic Web. The standards consist of two interrelated and complementary specifications: Direct Mapping of Relational Data to RDF and R2RML: RDB to RDF Mapping Language. In this paper we present initial results on the formal study of the R2RML mapping language by defining its semantics using Datalog. We prove that there are a total of 57 distinct Datalog rules which can be used to generate RDF triples from a relational table. Additionally, we provide insights on the relationship between R2RML and Direct Mapping.