Assembling a device

Abstract Presented here is a new way of reasoning about a device based on structure, which we call assembling a device . It consists of a symbolic combination of local qualitative constraints (confluences) leading to more global relations. Some reference variables are selected according to the task to be performed (simulation, observation, postdiction, …). The assembly step produces a set of equations expressing directly ‘internal’ quantities as functions of the reference quantities. We call such a set, a task-oriented assemblage . Then, determining the nonambiguous variables for a particular assignment of the reference quantities turns out to be straightforward. We can thus expect to perform qualitative reasoning on large systems. The assembly tool is a new rule, called the qualitative resolution rule . It has agreeable properties: (1) interpretation: each application can be interpreted as joining local descriptions to more global ones; (2) completeness: an assemblage provides all the nonambiguous variables for any assignment of reference variables. We show in the last part how these results could be extended to a framework dealing with orders of magnitude. In particular, this could provide an explanation for each possible behaviour in terms of the device structure.