Abstract. We explain a transformational approach to the design and verification of communicating concurrent systems. The transformations start form specifications that combine trace-based with state-based assertional reasoning about the desired communication behaviour, and yield concurrent implementations. We illustrate our approach by a case study proving correctness of implementations of safe and regular registers allowing concurrent writing and reading phases, originally due to Lamport.

This paper presents a transformational approach to the design of distributed systems where environment and concurrently running components communicate via synchronous message passing along directed channels. System specifications that combine trace-based with state-based reasoning are gradually modified by application of transformation rules until occam-like programs are achieved finally. We consider interactive and automatic aspects of such a design process and illustrate our approach by sketching the development of a shared register implementation.

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