Languages for Reactive Specifications: Synchrony Vs Asynchrony

Asynchronous and Synchronous languages have been in use for the speciication of reactive systems. One of the main distinguishing features of these two classes lies in the way nondeterminism is used for the specii-cation of programs. From this viewpoint, we analyze CSP (a typical asynchronous language) and Esterel (a synchronous language). The synchronous language Esterel is based on the notions of determinism, input nondeterminacy and parallelism whereas CSP is built on the notions of nondeterminism, concurrency and distribution. The main objectives of the study are to assess: 1. The role of nondeterminism in the speciication of the behaviour and realization of programs: A clear distinction between local and global nondeterminism enables us to distinguish between the implemen-tational nondeterminism and environmental or input nondeterminism. The results in this direction would enable one to achieve observable determinism where the implementational choices can be hidden and thus, analyze the program behaviour with reference to the real environmental nondeterminism in the speciication. This in turn leads to a proper reenement of speciications and programs and also aids in deriving distributed implementations of nite state transition systems which are not necessarily deterministic. 2. The implementability of asynchronous languages through synchronous languages: The synchrony hypothesis of the synchronous languages makes it closer to a perfect machine. Thus, the implementability of asynchronous languages in synchronous languages not only provides a realistic implementation but also provides other higher level abstractions (such as multi-process interactions) for reactive speciica-tions using features such as broadcast, interrupts, exception handling mechanisms etc.