The Process-Interaction-Model for a small example. In (a) a schematic diagram is shown, and in (b) the corresponding graph of the PIM for a small example system is given. Four processes are considered; 1: binding of molecule A (with site b1) to molecule R (site b1), 2: modification (e.g. phosphorylation) of site p1 of molecule R, 3: modification (e.g. phosphorylation) of site p2 of molecule R, 4: binding of molecule B with site b1 to phosphorylated R. Influences among the processes are depicted by green arrows in (a) and black arrows in (b). Binding process 1 has an influence on modification process 2. Process 2 and 3 mutually influence each other. Binding process 4 can only occur if the molecule R has been phosphorylated previously. This is emphasized by the arrow label AON (all-or-none). In the gray box at the upper left side next to the graph the molecules and their sites involved in the system are listed. Molecule A and B each have one binding site b1, the molecule R comprises one binding site b1 and two modification sites p1 and p2.