Why must the inputs and outputs always connect to opposite faces of a process?
It is necessary to graphical separate the connection of the links leading to entities pools in two sets, corresponding to the SBML’s “reactants” and “products”, or the BioPAX “left” and “right”. The image below presents a reversible reaction transforming A and B into C and D, or the opposite. On the left, the connections are separated in two opposite groups, and the meaning of the reaction is clear. On the right, on the contrary, each edge is connected to a different face of the process, and one cannot understand which entity pools are transformed into the others.
