The valid use of utility in adaptive real-time systems

Real-time systems that must adapt their behavior to changes in internal and external circumstances require flexibility in their scheduling. One approach that has been advocated for achieving this flexibility is called 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. There are simple tests for meaningful uses of values based on their scale types, and we apply these tests to investigate the meaningfulness requirements of some commonly-used scheduling approaches.