Canonical subgraph patterns in biological networks. Canonical subgraph patterns in biological networks. (a) Feed-forward loop (FFL): contains a "source" (at the top), "intermediate" (bottom-left), and "target" (bottom-right) nodes. (b) 3-cycle: a three node directed cyclic graph, (c) Single-input module (SIM). (d) Multiple-input module (MIM). (e) Bifan motif. SIM, MIM, and Bifan are two-layered graphs with edges from nodes in top- to bottom-layer. A Bifan is a MIM with exactly 2 parent and 2 child nodes.