Semantics of fault-tolerant actions in modechart

The semantics of a real-time system can be given by a set of relations governing the timing of the events that are significant to the system. An action is a pair of events: the start and stop events. The peculiarities of real-time applications dictate specialized semantics for actions with respect to criteria such as fault tolerance. In this gaper, we discuss the interaction between atomicity which is required for fault tolerance and the enforcement of timing constraints on actions. The graphical specification language Modechart is used as a concrete language for addressing the issues. We show that incorporating actions into specifications in general requires clairvoyance on the part of the implementation. The amount of clairvoyance can be limited by an Action Pruning theorem