In design environments, collaboration means more than the division of labor. It contains the notion of cooperation among agents with his or her independent intention. In a current design system, for example, VEXED (Steinberg, 1987), interactions with its user form a principal part of the design process. The design method which VEXED employed is top-down refinement plus constraint propagation. In this model of design process, the system decides what is possible and the user decides what is wise, that is, the user chooses which piece to refine next, out of all those still needing further refinement, and also chooses which way to refine it, out of all the alternatives that the system knows about that are consistent with the current constraints.