Projects providing RDF/SPARQL access to relational databases
- Revelytix Spyder is a free product for accessing various data sources, including databases, with SPARQL. It supports W3C's R2RML mapping language. Commercial support is available. Revelytix publishes a comparison of Spyder and D2RQ.
- Virtuoso RDF Views has pretty smart rewriting algorithms and also supports Named Graphs and W3C's R2RML mapping language (details). Commercial support is available.
- Sparqlify is an experimental RDB-RDF mapper. It was developed to allow SPARQL access to the OpenStreetMap database. It supports PostgreSQL databases and uses a concise, proprietary, SPARQL-based mapping language. It rewrites any supported SPARQL query into a single SQL query.
- ODEMapster is a database-to-RDF mapper that uses the R2O mapping language.
- Triplify, a small plugin for Web applications, reveals the semantic structures encoded in relational databases by making database content available as RDF, JSON or Linked Data.
- SquirrelRDF. In addition to relational databases, SquirrelRDF also supports access to LDAP directories.
- METAmorphoses publishes RDF generated from relational databases on the Web.
- DartQuery. DartQuery is a component of the DartGrid application framework which rewrites SPARQL queries as SQL against legacy relational databases.
- SPASQL is an open-source module compiled into the MySQL server to give MySQL native support for RDF.
- W3C maintains a list of R2RML and Direct Mapping implementations.
Publications about database-to-RDF mapping
This is a very incomplete list.
Standards and specifications
W3C's RDB2RDF Working Group develops standards for database-to-RDF mapping: