Recoverability of modular systems

GOSTELOW-VAN WEERT, it was shown that processes can be described by Petri-nets (PN). In this note we will demonstrate a way of designing programs using Petri-nets as a way of describing the desired behavior. This approach makes it possible to utilize all the theoretic knowledge developed for PN and thus provides a powerful tool for program design. In an example of this approach we show how to design a recoverable program. This design is based on a study of recoverable PN's presented in [2], [3], [4] and [5]. In this note, we will not deal with the code itself, but with the structural organization of the programs. Our approach is based on an hierarchical, top-bottom, modular design. At each level a description of the desired system behavior is given. This description is then modeled by a PN and analyzed using the theory developed for PN's. This analysis allows one to check for, among other things, properties of the systems such as recoverability, proper termination, etc. These properties are inherently structural and not dependent on internal module semantics.