The reference point for developing any artefact is its specification; to develop software formally, a formal specification is required. For sequential programs, pre and post conditions (together with abstract objects) suffice; rely and guarantee conditions extend the scope of formal development approaches to tackle concurrency. In addition, real-time systems need ways of both requiring progress and relating that progress to some notion of time. This paper extends rely-guarantee ideas to cope with specifications of—and assumptions about—real-time schedulers. Furthermore it shows how the approach helps identify and specify fault-tolerance aspects of such schedulers by systematically challenging the assumptions.

开发任何制品的参考点是其规格；要正式开发软件，需要正式的规范。对于顺序程序，前置条件和后置条件（以及抽象对象）就足够了；依赖和保证条件扩展了解决并发问题的正式开发方法的范围。此外，实时系统需要既要求进度又将进度与某种时间概念联系起来的方法。本文扩展了依赖保证的思想，以应对实时调度程序的规范和假设。此外，它还展示了该方法如何通过系统地挑战假设来帮助识别和指定此类调度程序的容错方面。