ABSTRACT

To live up to its promise of web-scale data integration, the Semantic Web will have to include the content of existing relational databases. One study determined that there is 500 times as much data in the hidden or deep web as there is in crawlable, indexable web pages; most of that hidden data is stored in relational databases [79]. Starting with a 2007 workshop, titled “RDF Access to Relational Databases”1, the W3C sponsored a series of activities to address this issue. At that workshop, the acronym, RDB2RDF, Relational Database to Resource Description Framework, was coined. In September 2012, these activities culminated in the ratification of two W3C standards, colloquially known as Direct Mapping [43] and R2RML [165].