Ultrawrap a "Virtual Triple-store for Semantic Web Data Management" exposes legacy data in relational databases as a triple-store without the need of replicating the data.

Existing commercial SQL query engines already subsume all the algorithms needed to support effective query rewriting from the SPARQL language (query language for the Semantic Web) to SQL.

UltrawrapCompiler is a related project focusing on the creation of a compiler that translates SPARQL queries to SQL queries for semantic web systems that are implemented using an RDBMS as a backend to hold RDF metadata.