employs a visual language as a high level specification tool for integrating existing software packages as built?in units. The built?in units cannot only be served as elements of a visual program, but also be used to provide computational details (e.g. textual code). Therefore high level modelling and low level specification are supported effectively. Moreover, levels and relations in PEDS facilitate program partitioning and mapping. Because the visual language integrates various software packages and the system environment into a uniform visual model, users can design, analysis, construct and test distributed computations without the need to transform or convert these packages across different platforms and languages.

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