Facebook reaches Social Graph database benchmark: Facebook engineers discuss the development processes behind LinkBench, and how it’s being used at the world's largest social network today.

Curtiss explained they serve a similar role, but these nodes have a numerical structure to them connecting them to the semantics of the Social Graph.

Curtiss explained they serve a similar role, but these nodes have a numerical structure to them connecting them to the semantics of the Social Graph.

Direct Acyclic Graph or DAG may be it. What is DAG? DAG is a directed graph data structure that uses a topological ordering. The sequence can only go from earlier to later.