Abstraction and Composition of Discrete Real-Time Systems

This paper extends the TTM/RTTL deductive and modelchecking framework for real-time reactive systems with a structured design method using the notions of real-time reactive modules, module abstraction and module composition. Equivalence transformations are used to obtain abstract systems, and a composition theorem is provided for deducing global properties from module specifications. The StateTime tool is used for checking module correctness. Abstraction and composition are applied to an actual industrial example involving the delay reactor trip for a nuclear reactor consisting of three independent microprocessors based controllers. Timing, concurrency, integer data, communication and nondeterminism are all important elements of the problem. While the StateTime tool can verify a single microprocessor controller (under 100k states and edges), the complete 3-version system suffers from a combinatorial explosion of states. By contrast, the proposed design method is able to verify the example, and scales up to larger systems.