ORGANIZATION OF DESIGN ACTIVITIES - OPPORTUNISTIC, WITH HIERARCHICAL EPISODES

The organisation of actual design activities, even by experts involved in routine tasks, is not appropriately characterised by the retrieval of pre-existing plans, but is opportunistic (possibly with hierarchic al episodes at a local level, but not globally hierarchical). Actually executed design actions depend, at each moment t, on the evaluation o f actions proposed at t-1. These proposals can be made by pre-establis hed plans, but also by other action-proposal knowledge structures. Thi s position is supported by results from diverse empirical design studi es. A major reason why design activities are organised opportunisicall y is that, even if designers possess plans which they may retrieve and use, the designers very often deviate from these plans so that their activities satisfy action-management constraints, of which the most im portant is cognitive economy. Two types of variables underlying this o pportunism are discussed: situational and processing. If design is opp ortunistically organised, a support system which imposes a hierarchica lly structured design process will probably handicap designers. Sugges tions for systems offering real support are formulated.