Simplex is a software architecture for dependable and evolvable process-control systems developed by the Software Engineering Institute. Our project consisted of creating a formal specification of this architecture, and analyzing its safety and liveness properties. We developed a Communicating Sequential Processes (CSP) model to describe the overall dynamic behavior of the Simplex architecture, which we verified using the Failure-Divergence-Refinement (FDR) model checker. As a result, we

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... red interesting things about the use of FDR that revealed subtle points in the Simplex architecture. We also developed a WRIGHT specification of this architecture to characterize precisely the connections between its components at the architectural level. The specification was based on the latest version of the CSP model. DecisionToUM.killCornplex ---KILLCOMPLEX) 1] DecisionToUM. kiliComplex -4 KILLCOMPLEX) WILLINGTOSTARTCOMPLEX 24 CMU/SEI-96-TR-006 Component SafetyController Port DeclareSafety = invoke -4 returnly -4 DeclareSafety Computation = DeclareSafety, invoke -Dec IareSaf ety. return! cntrl1o-ut-'; Computation CMU/SEI-96-TR-006 37 Acknowledgments