This article describes a method for representing and simulating ordinary di
fferential equation (ODE) systems which are imprecise - that is, where the
ODE model contains both parametric and functional uncertainty. Such models,
while useful in engineering tasks such as design and hazard analysis, are
not used in practice because they require either special structures which l
imit the describable uncertainty or produce predictions which are extremely
weak. This article describes SQSIM (for SemiQuantitative SIMulator), a sys
tem which provides a general language for representing and reasoning about
many common forms of engineering uncertainty. By defining the model both qu
alitatively and quantitatively and by using a simulation method that combin
es inferences across the qualitative-to-quantitative spectrum, SQSIM produc
es predictions that maintain a precision consistent with the model imprecis
ion. (C) 1998 Elsevier Science Ltd. All rights reserved.