The specification method for real-time software presented in this tutorial has been partly described by the authors in other published reports. The method centers around a hierarchy of automata, in which multiple states can be active at any moment of time and multiple transitions can fire simultaneously. The states at any level can be decomposed into lower-level machines in such a manner that each higher-level specification imposes constraints on those at lower levels. Thus the machines at higher levels may act as “policy machines” that both define requirements and suggest how requirements can be achieved. A method is presented such that when a choice of actions to reach a goal state is known, the ordering and intermediate delays between the actions necessary to meet given constraints may be derived.

The method is sketched in fair detail, in terms of explanations, definitions, and graphic illustrations. The presentation ends with a demonstration of its application to a realistic sample problem. The introduction characterizes the method in comparison with a number of other previously published methods. What is missing, however, is a comparison with how these other methods would help to solve the sample problem, and even more, how the present method would compare with other methods in actual application by working programmers. Because of these omissions, the significance of the contribution remains uncertain.