Top-down design in the context of parallel programs

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A class of parallel programs, based on Free Choice Petri nets, is modeled by associating operators and predicates with vertices of the net. The model, called a formal parallel program (FPP), forms a natural extension of flow-chart notation to parallel programs. Definitions are made of the behaviour of an FPP, and the simulation of one FPP by another. A class of top-down FPPs is next defined, by requiring program graphs to be obtained through successive refinement steps, using a restricted set of control structures. Using the above definitions, it is shown that there exists an FPP ℰ satisfying the property that for any top-down FPP ℰ′ simulating ℰ, the degree of parallelism attainable in ℰ′ is smaller than that in ℰ. The measure of parallelism used is the number of different ways of carrying out a computation. In the case of parallel programs, this phenomenon of loss of parallelism therefore uncovers a performance factor which may offset some of the advantages of using top-down design. © 1979 Academic Press, Inc.

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Information and Control