Combining Look-ahead Design-time and Run-time Control-synthesis for Graph Transformation Systems.

AbstractThe correct operation of safety-critical cyber-physical systems is crucial. However, such systems often feature a large variability of start configurations, an intractably large state space, a high degree of uncertainty, or inherently unsafe behavior. A model of the expected system behavior starting in the current state can be used by look-ahead controllers to derive control decisions to avoid paths to safety violations when possible. However, the computational effort for deriving and analyzing the future system behavior is exponential in the look-ahead.In this paper, we employ Graph Transformation Systems (GTSs) for the modeling of expected system behavior. We then combine design-time and run-time control synthesis based on Supervisory Control Theory (SCT) achieving an exponential cost-reduction for a given controller look-ahead. For a fixed required reaction time of controllers, much longer look-aheads may therefore be employed. To illustrate and evaluate our approach, we consider a system where shuttles must avoid collisions with ambulances at level crossings.