new sample project demonstrating Datomic as a ‘graph database’

inspired from the [Neo4j tutorial](http://www.neo4j.org/learn/cypher)

The sample graph contains actors and movies as nodes and the ‘acts-in’ relationship as edges. The information about edges are stored in the transaction that recorded the edge.



> http://thornydev.blogspot.com/2012/06/datomic-initial-analysis.html
> …
> Stu pointed out that one difference between Datomic and a graph database like Neo4j is that the latter "reifies edges". In graph theory you have two basic concepts: the Node (Vertex) and the Relationship (Edge) between two Nodes. Both are first class (reified) entities of the graph model - they can have identities and attributes of their own.
>
 >Datomic does not make the Relationship a thing unto itself - it is just the "ref" between two entities (nodes). In Stu's words: "We believe many of the common business uses for reified edges are better handled by reified transactions".
> …