On the design of systems of cooperating functional processes

This paper describes a design concept for systems of cooperating distributed processes based on a variant of coloured Petri-nets. It cleanly separates graphical specification of processes and their interaction (or communication) from the algorithmic specifications of the computations that need to be performed by the individual processes. Designing complex process systems is aided by abstractions similar to those that are available in programming languages. In conjunction with a small set of well-defined interaction schemes for process communication it ensures well-behaving systems largely by construction. Essential invariance properties of small subsystems which in incremental steps may either be verified by formal methods or validated by simulation are not corrupted when embedding them in the context of larger systems. The paper focuses particularly on the construction of large systems by recursive abstractions of small net templates which, at execution time, may be recursively expanded to distribute application problems evenly over several processing sites for concurrent processing.