This paper describes how to use an assumption-based truth maintenance system (ATMS) to significantly speed up qualitative reasoning. Specifically, we introduce three organizing abstractions for ATMS-based problem solvers (many-worlds databases, justify/interpret cycles, and closed-world tables). We illustrate their utility by describing the Qualitative Process Engine (qPE), an implementation of Qualitative Process theory that is roughly 95 times-faster and signficantly simpler than the previous implementation. After analyzing gPE's performance, we draw some general conclusions about the advantages and disadvantages of assumption-based truth maintenance systems. Program:ENGINEERING

Abstract: One main problem in qualitative simulation is that it often produces too detailed qualitative descriptions of a system's possible behaviors, or produce a lot of behaviors that differ very slightly. This paper addresses the problem of summarizing the result of a qualitative simulation to make it more perspicuous. Twocauses of behavior proliferation have been identified and two algorithms to aggregate behaviors that do not differ significantly are presented. Simple-xamples are used to illustrate the functionning ofeach algorithm.