Engineering Design through Constraint-Based Reasoning

application of constraintbased reasoning to parametric engineering design (Murtagh 1991).1 It deals with the practical application of constraint networks, using automated reasoning to overcome some of the blind spots in conventional iterative design. Parametric engineering design refers to routine-level design (Brown and Chandrasekaran 1985) in which the parameters and variables describing the design object are known, and the problem is one of finding a consistent set of parameter values that conform to specified requirements. It involves converting a well-established symbolic representation of an object, consisting of a set of parameters and variables, into a specific numeric representation. This conversion involves the attachment of numeric values to the parameters and the use of analysis programs to either verify the consistency of these values or eliminate inconsistent values. Conventional methods of parametric design rely on the iterative reuse of analysis programs to converge on a satisfactory solution. Finite-element and other analysis programs require considerable computer resources; are unidirectional; and are inflexible in that they require a complete reprocessing, irrespective of how small the change is that was made to the previous design description. Furthermore, exact values are required, and imprecise data cannot be dealt with. My research proposes a general method to minimize the use of the analysis programs and enable bidirectional reasoning by availing of constraint-based reasoning to carry out redesign (Murtagh and Shimura 1990, 1991). A problem solver, consisting of constraint networks that express basic relationships between individual design parameters and variables, is attached to the analysis programs, so that these programs can provide initial values for the parameters. In redesign and optimization, however, the networks alone can then reason about required adjustments to find a consistent set of parameter values.