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.
R. Angles, and C. Gutierrez. The Semantic Web: Research and Applications, volume 3532 of Lecture Notes in Computer Science, Springer Berlin Heidelberg, (2005)