Verifying process models built using parameterized state machines

Software process and work flow languages are increasingly used to define loosely-coupled systems of systems. These languages focus on coordination issues such as data flow and control flow among the subsystems and exception handling activities. The resulting systems are often highly concurrent with activities distributed over many computers. Adequately testing these systems is not feasible due to their size, concurrency, and distributed implementation. Furthermore, the concurrent nature of their activities makes it likely that errors related to the order in which activities are interleaved will go undetected during testing. As a result, verification using static analysis seems necessary to increase confidence in the correctness of these systems. In this paper, we describe our experiences applying LTSA to the analysis of software processes written in Little-JIL. A key aspect to the approach taken in this analysis is that the model that is analyzed consists of a reusable portion that defines language semantics and a process-specific portion that uses parameterization and composition of pieces of the reusable portion to capture the semantics of a Little-JIL process. While the reusable portion was constructed by hand, the parameterization and composition required to model a process is automated. Furthermore, the reusable portion of the model encodes the state machines used in the implementation of the Little-JIL interpreter. As a result, analysis is based not just on the intended semantics of the Little-JIL constructs but on their actual execution semantics. This paper describes how Little-JIL processes are translated into models and reports on analysis results, which have uncovered seven errors in the Little-JIL interpreter that were previously unknown as well as an error in a software process that had previously been analyzed with a different approach without finding the error.