An environment to support designers in the modeling, analysis, and simulation of concurrent systems is described. It is shown how a fully nested structure model supports multilevel design and focuses attention on the interfaces between the modules which serve to encapsulate behavior. Using simple examples, it is shown how a formal graph model can be used to model behavior in three domains: control flow, data flow, and interpretation. The effectiveness of the explicit environment model in SARA is discussed and the capability to analyze correctness and evaluate performance of a system model is demonstrated. A description of the integral help designed into SARA shows how the designer can be offered consistent use of any new tool introduced to support the design process.