  We discuss a notion of clustering for directed graphs, which describes how
likely two followers of a node are to follow a common target. The associated
network motifs, called dicliques or bi-fans, have been found to be key
structural components in various real-world networks. We introduce a two-mode
statistical network model consisting of actors and auxiliary attributes, where
an actor i decides to follow an actor j whenever i demands an attribute
supplied by j. We show that the digraph admits nontrivial clustering properties
of the aforementioned type, as well as power-law indegree and outdegree
distributions.
