Integrating state machine analysis with system-theoretic process analysis

Safety becomes a critical aspect for software-intensive systems in different applications areas. Many hazard analysis techniques are proposed and used to investigate system design models to elicit hazards and design flaws. STPA (System- Theoretic Process Analysis) is a modern hazard analysis technique, which is based on a new systems-theoretic model of accidents for large and complex systems. With STPA, the system is viewed as interacting control loops and the accidents are considered as results from inadequate enforcement of safety constraints in design, development and operation. STPA still needs appropriate diagrammatic notations to represent the relation between the process model variables, control actions and hazards. For this purpose, we propose to integrate state machine analysis with STPA to provide a suitable notation of arguments between the states of controllers, control actions and hazards.