Introduction to Graph Databases
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Introduction to Gremlin
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Thank you again to Groupon Engineering! They hosted our Graph Database Meet-up at their Headquarters.
Join us May 31st, 2012 for our next meet-up Add data from your existing Application into Neo4j.
Max De Marzi 
Is it possible for a node to be an edge, and vice versa? And can a node be a subgraph?
Nope. However graphs are not two dimensional, you can have layers of graphs connected by different relations. For example a group layer that sits on top of users, and organizations on top of groups, which lets you treat nodes as entry points into subgraphs.