Integrating functional models and structural domain models for diagnostic applications

In diagnostic applications knowledge of the function of a device, or what the device is intended to do, can be very important However, many modelbased diagnostic systems rely solely on knowledge about the structure of a device and how the components of that device behave. The operation of the whole device is then synthesised from this information. This type of system only represents knowledge of the how the system works type, not of the what it is for type. However, diagnostic engineers do not just use structural knowledge — they also use knowledge about the function of a device—something which is beyond the scope of a purely structural model-based system. If second generation expert systems are to emulate the capabilities of human experts; they too must be able to reason about the structure of the device and the function of the device. In this chapter we consider why knowledge of the function of a device is important for diagnosis. We then present some of the issues involved in any system which integrates multiple domain models. The Integrated Functional and Structural Modelling system we have developed is then introduced and a diagnostic system built around this approach is presented.