Component-ontological representation of function for reasoning about devices

We propose principles behind component-ontological representation of function. In this representation, the function of a component is expressed in terms of its ports. The representation has many advantages: (i) The function of a component can be represented in isolation of its environment. Therefore, libraries of function models can be built. These models are re-usable. (ii) The function model of a complex device can be built by composing the function models of its components. This helps preserve the fidelity of representation. Further, this process can be automated. (iii) The representation is linear in space complexity: the function model of an atomic component is linear in the number of its ports, and that of a composite device is in most cases linear in the number of its components. We propose Classes as a component-ontological representation of function. We illustrate Classes by using it to model parts of a printer buffer, which has the complexity of a microcomputer. We also demonstrate how class models may be used for model-based diagnosis.