Virtuoso is a high-performance object-relational SQL database.
As a database, it provides transactions, a smart SQL compiler, powerful stored-procedure language with optional Java and .Net server-side hosting, hot backup, SQL-99 support and more.
It has all major data-access interfaces, such as ODBC, JDBC, ADO .Net and OLE/DB.
OpenLink Virtuoso supports SPARQL embedded into SQL for querying RDF data stored in Virtuoso's database.
SPARQL benefits from low-level support in the engine itself, such as SPARQL-aware type-casting rules and a dedicated IRI data type.