How Things are Intended to Work: Capturing Functional Knowledge in Device Design

When designing a device, the final product of the design process is usually considered to be a physical specification of a device. However, the design of the causal mechanism underlying the physical specification, i.e. how the device is intended to work to achieve its function, is a product just as important as the physical specification, if not more. Capturing this knowledge of causal mechanism is necessary in order to understand the physical specification of the device as well as to evaluate and refine the specifications during the design process. Despite the importance of such knowledge, existing CAD tools do not support its explicit representation or manipulation. We describe a design support system under development in which knowledge of both the causal mechanism and the physical structure of a device being designed is explicitly represented and manipulated. The system allows the designer to provide functional specifications at various levels of abstraction in a language called CFRL (Causal Functional Representation Language). The CFRL specification acquired from the user enables the system to evaluate the physical specification as it is being developed in order to provide useful feedback to the designer. Furthermore, functional specifications provide an important basis for recording the engineer's design rationale.