An Explication of Function

For the last several years, mostly motivated by diagnostic and design problem solving, there has been much work on functions of devices. The intuitions about functions that these investigations capture and to some extent formalize are not all the same, and are generally quite restricted in their range of applicability. In this paper, we attempt to provide a foundation for unifying and generalizing many of these intuitions. Objects are embedded in an environment and represented in a view. Objects have properties in causal interaction with environment properties and are characterized by their property relations. Functions are defined in terms of the effects objects have on their environment. This framework is sufficient to unify static and dynamic objects, abstract and physical objects, intended and natural functions, and structural explanation as a species of causal ordering. We believe that with additional domain-specific content theories at different levels of abstraction, this framework can be uniformly applied in different domains. 1. Desiderata for a Framework on Functions The last two decades have seen flowering of work on reasoning about physical systems. Recently, motivated by problems in diagnosis and design, a stream of work has emerged in which the notion of device function has been central. Diagnosis is naturally concerned with malfunctions, and design is, of course, concerned with producing a structure that has a desired function. This stream of work uses many of the ideas that have been developed in qualitative reasoning and qualitative simulation. For example, [1] uses qualitative simulation to verify design functions. The various investigations on device functions have mostly lacked a unified technical vision underlying them. Different intuitions about functions are pursued in different contexts and application domains. It is hard to see how to unify them and build on each other, even though each approach clearly solves some set of problems. What we need is a minimalist effort, something that looks for what is common among all the intuitions about function and seeks to build the smallest ontological framework within which the notion of function can be explicated. Of course, for work in particular domains and applications, additional constructs and content theories will be needed, but, if the effort is successful,