Shortcomings of qualitative simulation and of quantitative simulation motivate combining them to do simulations exhibiting strengths of both. The resulting class of techniques is called semi-quantitative simulation. One approach to semi-quantitative simulation is to use numeric intervals to represent incomplete quantitative information. In this research we demonstrate semi-quantitative simulation using intervals in an implemented semi-quantitative simulator called Q3. Q3 progressively refines a qualitative simulation, providing increasingly specific quantitative predictions which can converge to a numerical simulation in the limit while retaining important correctness guarantees from qualitative and interval simulation techniques. Q3's simulations are based on a technique we call step size refinement. While a pure qualitative simulation has a very coarse step size, representing the state of a system trajectory at relatively few qualitatively distinct states, Q3 interpolates newly explicit states between distinct qualitative states, thereby representing more states which instantiate new constraints, leading to improved quantitative inferences. Q3's techniques have been used for prediction, measurement interpretation, diagnosis, and even analysis of the probabilities of qualitative behaviors. Because Q3 shares important expressive and inferential properties of both qualitative and quantitative simulation, Q3 helps to bridge the gap between qualitative and quantitative simulation. (C) 1997 Elsevier Science B.V.
