R2RML is a W3C candidate recommendation language for expressing customized mappings from relational databases to RDF datasets. Such mappings provide the ability to view existing relational data in the RDF data model, expressed in a structure and target vocabulary of the mapping author’s choice. R2RML mappings are themselves RDF graphs and written down in Turtle syntax that enable different types of mapping implementations. The Incubator Group has issued a survey (Sahoo et al., 2009) of current approaches for mapping Relational Databases to RDF, in which various techniques and systems available to the community for mapping RDB to RDF are reviewed. This survey also included the definition of a reference framework consisting of six components that allowed the effective categorization and comparison of different approaches used in mapping RDB data to RDF. These individual
components are: