Eliminating the ´hard´/´soft´ real-time dichotomy

A brief and informal overview is given of a new framework which permits timeliness to be expressed and enforced for the whole real time continuum in a well defined and general way. The framework has been successfully implemented and used experimentally. The new model of timeliness which was created is called the benefit accrual model. It is a framework for expressing timeliness requirements across a wide spectrum of real time hardness and softness in a unified and well defined manner-timeliness is a continuum of softness, in which ´hard´ is one end point. This model is a generalisation of the earlier time value functional model (E.D. Jensen et al., 1985) in the Alpha kernel. The framework is based on three orthogonal functions for specifying timeliness: the time constraint for individual computations; the collective timeliness of a set of computations; and the acceptability of collective timeliness of a set of computations. First, the author introduces the idea of timeliness as a scoped attribute of a computation.