The Measurement and Usage of Utility in Adaptive Real-Time Systems

Real-time systems that must adapt their behaviour to changes in internal and external circumstances require flexibility in their scheduling. One approach that has been advocated for achieving this flexibility is called `utility', or `value-based' scheduling, wherein services are distinguished based upon their current utility values. The main result of this paper is that the assumptions used in the assignment of these values must be matched with the way the values are used in scheduling. The key notion for ensuring this is the `scale type' of the value, in the sense defined by measurement theory. For single-criterion values there are simple tests for `meaningful' uses of values based on their scale types, and for multiple-criteria values, the scale type is determined by the function combining the criteria and their individual scale types. This paper establishes the theoretical link between the assignment and use of values, and also proposes a procedure for assigning values within a sound mathematical framework.