relationaltoRDF

RelationaltoRDF is the process of converting data stored in relational databases into the Resource Description Framework (RDF) used by the Semantic Web. The aim is to enable interoperable data integration, reasoning, and querying across diverse data sources by representing tabular data as a graph of RDF triples.

There are several approaches to relationaltoRDF. The RDB2RDF family includes standards and tools designed to map relational schemas to RDF. The W3C standard R2RML (RDB to RDF Mapping Language) defines a declarative mapping from database tables, columns, and relationships to RDF triples, supporting subject generation, predicate selection, object creation, and the use of named graphs. Direct Mapping is a simpler approach that relies on a straightforward correspondence between schema components and RDF terms. Other tools such as D2RQ, Virtuoso RDF Views, and Ontop implement mapping or on-demand querying of relational data as RDF.

In a typical workflow, a database schema is analyzed to produce mapping rules that translate rows into subjects, columns into predicates, and cell values into objects. Subjects are often derived from primary keys or URIs, predicates from column names or ontology terms, and objects from literal values or linked resources. Mappings commonly reuse standard vocabularies and domain ontologies to promote data interoperability, and the resulting RDF graph can be exposed via SPARQL endpoints, RDF dumps, or virtual graphs.

Benefits include enabling Linked Data publication, cross-database integration, and semantic querying, while challenges involve maintaining mappings as schemas evolve, handling large-scale data, preserving data provenance, and representing complex relational constructs such as many-to-many relationships and NULL values. See also RDF, SPARQL, R2RML, D2RQ, RDB2RDF.