Sail is an RDF triple/quad store interface developed by OpenRDF. Any database the implements the Sail interfaces properly is a valid RDF triple/quad store. A graph database is a great way to build a triple/quad store because its possible to mix indexing and graph traversals to solve the RDF “pattern match” problem.
A. Cal\`ı, G. Gottlob, und T. Lukasiewicz. Proceedings of the 12th International Conference on Database Theory, Seite 14--30. New York, NY, USA, ACM, (2009)