Real time: further misconceptions (or half-truths) [real-time systems]

J.A. Stankovic (see ibid., vol. 21, no. 10, p. 10-19, 1988) analyzed some common misconceptions about real-time computing. His analysis addressed the very notion of real-time computing and touched upon the applicability of concepts that have proven useful in nonreal-time modeling of reactive systems, such as interleaving models, nondeterminism, and fairness. From his viewpoint, such concepts are no longer appropriate when real time is a concern, and a new set of abstractions must be devised. The author addresses these issues from the viewpoint of theories and formal modeling. By analyzing some common sources of misunderstanding, he shows that some common statements about real-time modeling are unjustified, or express only half-truths. A potential source for misunderstanding Is the restricted practical interpretation of theoretical notions. With limited experience in using theories of computation, we can easily mistake a theoretical construct for the reality of a program. As pointed out by Stankovic, the special role of time in real-time systems easily leads to incompatibilities between nonreal-time and real-time models. There are approaches where the transition from nontimed to timed models is smooth, however, and where the above theoretical notions are also meaningful in the presence of metric time. Since specification and design of real-time systems may involve both nontimed and timed levels of abstraction, the compatibility of these levels seems important.<>