FYI: See this recent paper by Google Research and IBM Watson Research:

SQLGraph: An Efficient Relational-Based Property Graph Store http://research.google.com/pubs/archive/43287.pdf

Previous discussion: https://news.ycombinator.com/item?id=11101013

I mean, I was putting a graph in PostgreSQL, I don't know if that makes it a "graph database". Table of nodes, table of edges.