We have persistent layer implemented by JPA. I understand JPA came out with relational DB in mind. But I believe this is an important feature which graph DB needs to consider if it want to be adopted widely. Neo4j has some sort of JPA support. Oracle EclipseLink already has extension to the spatial graph data. Empire http://github.com/clarkparsia/Empireis an implementation of the JPA for RDF and the Semantic Web. I wish Oracle has similar thing as soon as possible.