PC: A Compiler from Physical Models into Qualit at ive Different ial Equations*

Qualitative reasoning can, and should, be decomposed into a model-buibding task, which creates a qualitative differential equation (&DE) as a model of a physical situation, and a qualitative simuhtion task, which starts with a QDE, and predicts the possible behaviors following from the model. In support of this claim, we present &PC, a model builder that takes the general approach of Qualitative Process Theory [Forbus, 19841, describing a scenario in terms of views, processes, and influences. However, &PC builds &DE s f or simulation by QSIM, which gives it access to a variety of mathematical advances in qualitative simulation incorporated in QSIM. We present QPC and its approach to Qualitative Process Theory, provide an example of building and simulating a model of a non-trivial mechanism, and compare the representation and implementation decisions underlying &PC with those of QPE [Falkenhainer and Forbus, 1988; Forbus, 19901.