Advice on representing and querying graphs?

We are about to start a project that builds a social network. There
is a symmetric and transitive relationship LinkedIn-like “is contact

At any given time we need to know the size of someone’s network, be
able to determine whether someone is contact of someone, and most
importantly to be able to bound searches to someone’s network.

Given those requeriments the representation of the graph seems
crucial a priori. Do you have any advice on how to implement that
with AR?

– fxn