Summary: SyncCharts: A Visual Representation of Reactive Behaviors
October 1995, revision April 27, 1996
This report is an introduction to SyncCharts (Synchronous Charts) a new graphical representation
of reactive behaviors based on the synchronous paradigm. Syntactically this model is close to State-
charts and Argos. It o ers enhanced preemption capabilities. Its semantics is formally de ned and any
Synchronous Charts can be translated into an equivalent Esterel program.
SyncCharts combines state-oriented descriptions, hierarchy and powerful preemption mechanisms. It
is fully compatible with the imperative synchronous language Esterel and it encourages programming
with both textual and graphical reprensentations.
A reactive system maintains permanent interactions with its environment. Usually, reactive systems are
concurrent systems. Their globalbehavior results fromthe cooperation of their components (subsystems). In
order to carry out an expected behavior, the evolutions of subsystems must be coordinated. Communication
(information exchange) plays a central role in this coordination, and consequently, reactive systems are
often viewed as communicating processes. This approach relegates preemption to a position of secondary
importance, which is prejudicial to manyreactive applications. \A process preemption ...consists in denying
the right towork to a process, either permanently(abortion)or temporarily(suspension)" (G. Berry Ber92]).
Real-time operating systems, interrupt-driven systems, and more generally, control-oriented systems heavily