Temporal uncertainties in interactions among real-time objects

A model of a distributed real-time system which supports reasoning about the consistency and accuracy of real-time data and about the performance of real-time communication protocols is presented. The conventional object model is extended into a model of a real-time (RT-) object which incorporates a real-time clock as a mechanism for initiating an object action as a function of real time. The notion of accuracy as referring to the time gap between a state variable in the external world and its representation in a real-time computer system is adopted. The effects of the temporal uncertainties of different classes of communication protocols on the consistency and the accuracy of RT-objects are analyzed. Finally, an approach to structuring fault-tolerant RT-objects in the form of active object replicas is discussed, and the effects of a failure of a task in a replica on the responsiveness of remote objects are analyzed