i . ' il ' . Imprecise Results : Utilizing Partial Computations in Real - Time Systems

In real-time systems, a computation may not have time to complete its execution because of deadline requirements. In such cases. no result except the approximate results produced by the computation up to that point will be available. It is desirable to utilize these imprecise results if possible. We propose two approaches to enable computations to return imprecise results when executions cannot be completed normally. The milestone approach records results periodically. and if a deadline is reached, returns the last recorded result. The sieve approach demarcates sections of code which can be skipped if the time available is insufficient. By using these approaches, the system is able to produce imprecise results when deadlines are reached. We describe the design of the Concord project which supports imprecise computations using these techniques. We also present a general model of imprecise computations which takes into account the influence of the environment, and show where our approach fits into this model.