MORE-OR-LESS FOLLOWING A PLAN DURING DESIGN - OPPORTUNISTIC DEVIATIONS IN SPECIFICATION

An observational study was conducted on a mechanical engineer throughout his task of defining the functional specifications for the machining operations of a factory automation cell. The engineer described his activity as following a hierarchically structured plan. The actual activity is in fact opportunistically organized. The engineer follows his plan as long as it is cognitively cost-effective. As soon as other actions are more interesting, he abandons his plan to proceed to these actions. This paper analyses when and how these alternative-to-the-plan actions come up. Quantitative results are presented with regard to the degree of plan deviation, the design components and the definitional aspects which are most affected by these deviations, and the deviation patterns. Qualitative results concern their nature. An explanatory framework for plan deviation is proposed in the context of a blackboard model. Plan deviation is supposed to occur if the control, according to certain selection criteria, selects an alternative-to-the-planned-action proposal rather than the planned action proposal. Implications of these results for assistance tools are discussed briefly. © 1990 Academic Press Limited.