DUALITY: An Architecture Independent Design Model for Parallel Systems Based on Partial Orders Semantics

This paper introduces DUALITY, a design model that provides a more structured style of parallel programming and re nes causality from concurrency. We investigate semantic and syntactic transformations that support identifying the structure of a parallel program, as the basis for reducing the design complexity. The initial focus is on speci cation and correctness, then gradually adding architectural details and nally addressing e ciency. A parallel program is viewed as a MetaProgram the result of causally composing an architecture-independent algorithm the speci cation, with an architecture-dependent program the mapping. This approach supports the derivation of e cient parallel implementations from program speci cations. Consequently, transparent and architecture-independent speci cations can be transformed into forms that match particular target architectures. Correctness of the implementation is inferred from correctness of the speci cation, by gradually imposing temporal and causal order and by transforming any property of the speci cation into a property of the parallel program. DUALITY relates data and process parallelism and aims to reuse design knowledge from sequential patterns. DUALITY is developed in the context of the UNITY formalism and the principle and algebraic laws of Communication Closed Layers (CCL), and illustrated through the algorithm of all-points shortest path.