Why Graph?
Graph is the natural abstraction of relationship. Relational database has been adapted to represent relation due to the lack of better technology. Relational database is a synthetic way to represent relationship and makes it extremely hard/impossible to figure out deeper relationship between information beyond a few levels.
Lack of mature graph databases and industry standards were the main reasons hindering the growth of graph-based software products. This limitation is getting addressed by the successes of graph databases like Neo4j and OrientDB.
