A method for facilitating the specification and analysis of semihard real-time systems is described. The authors introduce the notion of an activity, the fundamental unit of computation upon which the methodology is based. They present a notation for creating an integrated requirements model which addresses the functional, behavioral, temporal, and information aspects of a semihard real-time system. It is shown how the fundamental properties of a requirements model can be analyzed. Extensions of the activity formalism to other classes of semihard real-time systems are considered. The authors show that this approach can be used to specify adaptive as well as periodic and sporadic computations.>

An investigation is presented of the relationship between external inputs and the demands imposed on the various resources in advanced sensor systems. This reveals the deficiency of the classical execution model for hard real-time systems, consisting of periodic and sporadic tasks, for modeling the workload in such systems. The classical model is extended with additional attributes for describing the behavior of tasks and with another type of task, adaptive tasks, which are repetitive but not strictly periodic. Notation is presented for specification of computational activities and the dynamic behavior of software in such systems. Also proposed is a multilevel scheduling structure for scheduling system resources (e.g. processors, sensors, and memory).>