(For reference, according to Facebook engineers, the Social Graph is a graph data structure involving an "immense map" of people, places, and things and the connections between them.) ...

Dynamic graph algorithms and data structures represent a vital research frontier in computer science, underpinning applications from network analysis to real-time system monitoring.

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.

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.

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.