statecharts for Reconfigurable Control of Complex Reactive Systems: a new formal verification methodology

Several formalisms are available for the specification of control in complex reactive systems. Statecharts are increasingly being proposed as the language of choice. Limitations of these formalisms in the context of formal verification have been discussed in an accompanying paper. Formal verification is necessary to specify these systems in an easy and safe way, to maintain traceability along the different phases of the design, and to analyse the behaviour of the defined system. The current communication reports a new approach for modular specification and verification of statechart based controllers for systems characterised by continuous reaction to external stimuli and asynchrony. We start from the methodology of Drusinsky and Harel to develop a statechart into a tree of interconnected FSMs: each state at each non-atomic level of the statechart hierarchy is represented by a machine implementing the FSM corresponding to its sub-states on the next immediate level. The methodology proposed in the present paper is based on: (i) a modified definition of controllability (as suggested by Fiordal, et al for unequal alphabets) from that in standard supervisory control theory; (ii) prioritized synchronization of Heymann instead of Ramadge-Wonham type supervisors and event forcing supervisors of Golaszewski-Ramadge to handle the resulting nondeterministic systems with driven events; (iii) disjunctive and mixed fusion rules of LaFortune et al to handle the state space explosion in real-scale applications and (iv) the mechanism of inter-modular communication through port structures developed by Endsley et al. The proposed new synthesis successfully confronts the modular verification/implementation problem for statecharts