Design histories in conventional CAD or tool-based CAD frameworks, capture how the design was created in the form of a sequence of commands or tool invocations, but they do not capture "why". This research develops an interactive design decision-making framework in which the history of the design process captures not only "how," but also "why" the design product has the current form. The main characteristic of the approach is that objectives (which describe intent) are used to define the design problem and represent intermediate stages leading to the final solution. Objectives are relationships over variables describing the space of product descriptions. Objectives may be constraints or they may involve minimizing or maximizing the value of a design variable. The designer manipulates the design only through changes to the objectives and cannot directly alter the design product description. The approach is systematic involving the generation, evaluation and selection of alternatives at each decision step. The designer interacts with the decision-making process by defining or identifying operators for achieving objectives and by guiding the selection of alternatives.;The history of the design process is recorded in a representation called the design record. The design record provides: (1) an organized history of the design decision-making process; (2) an explicit representation of the objectives and their alternative decompositions; (3) the ability to backtrack to explore different alternatives generated at previous decision points; (4) the ability to determine all decisions that might be affected when changes are made; and (5) the facility to replay portions of the recorded history. An interactive computer-based environment has been developed to demonstrate this approach for the design of spatial layouts for residential buildings.
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