PROCESS TRANSITION NETWORKS - A FORMAL GRAPHICAL KNOWLEDGE REPRESENTATION TOOL

A formal definition of Process Transition Networks (PTNs), recently introduced by Sandewall [San90], is presented. PTNs may be used as a graphical language to describe complex, qualitative processes; processes, which are difficult to express quantitatively even with the help of causal dependencies. The formal definition of the language is based on graph theory, and has strong similarities with Petri net theory. PTNs are first introduced informally, followed by syntactic and semantic specifications. The relation between PTNs and Petri nets is considered, and 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.