Process transition networks: what are they for?

Process transition networks (PTNs) are a graphical language to describe complex qualitative processes, processes which are difficult to express quantitatively even with the help of causal dependencies. Road or air traffic monitoring, process control and computer systems maintenance are examples of possible application areas for PTNs. The language primitives are introduced informally, followed by an example of a more complex nature. The relation between PTNs and Petri nets is considered. It is shown that although PTNs have no more expressivity than Petri nets, their flexibility as a representation language for complex processes justifies their existence