Modeling structures like the social graph of Facebook, connections to friends and their acquaintances, or your follower structure on Twitter is surprisingly difficult with traditional databases. Trying to map a network path – easily represented with squiggles and arrows on a whiteboard – with a relational model inevitably leads to performance-hungry join statements, the natural enemy of responsive websites.
The Neo4j 
graph database natively stores graph models and offers fantastic performance – as long as you don’t overcook the complexity of the queries. Its generic storage model consists of nodes and relationships. Both can possess attributes; for example, a node that represents a person could contain a
field for storing the name or carry a relationship
and its intensity (