After evaluating several graph databases, I decided to put more emphasis on Neo4J. Neo4J seems to be better documented and has a better REST API than the others. But still, I did not want to move all my relational data to Neo4J and there was actually no need to do so. I only needed the graph functionality of Neo4J to retrieve the user relationships as a resultset and merge it with my good old relational data. So I decided to go on to my evaluation by preparing a small .Net assembly to access Neo4J REST API and make use of the CLR functionality in SQL Server.