On the Combination of Synchronous Languages

Synchronous languages [1], [4], [7], [9] address the specication and programming of reactive processes, i.e. processes which continuously respond to stimuli at a rate determined by the environment. The synchrony hypothesis [1] states that a process is fully responsible for the synchronization with its environment, that is: event synchronization: the process is always able to react to events of the environment at a rate determined by the environment;response synchronization: the response synchronizes properly with the environment, i.e., the time elapsed between a stimulus and the response of the process is short enough (relatively to the dynamics of the environment) so that the environment is still receptive to the response. Furthermore, the behaviour of a process should be reproducible with regard to input events, or, in more technical terms, deterministic. Both these requirements are prerequisites for the dependable service of a process, for instance as controller in a safety-critical environment such as an automobile, an aircraft, or a power station.