A Formal Analysis Framework for PLEXIL

The Plan Execution Interchange Language (PLEXIL) is a rich concurrent and reactive language developed by NASA to support autonomous commanding and monitoring for a variety of space systems. In this paper, we propose a semantic framework for the analysis of PLEXIL. In particular, the semantic framework allows for the formal study of properties such as determinism, compositionality, run to completion, termination, and stuttering, for different variants of the language. The framework is organized as a stack of abstract execution relations that define the small-step semantics of a synchronous event-driven language. This modular presentation of the language semantics enables the instantiation of the framework to different semantic variants of PLEXIL, and therefore, the framework serves as a formal designing tool. The mathematical development presented in this paper has been formalized and mechanically checked in the Program Verification System (PVS).