stances. Knowledge becomes structured only in response to some specific problem to be solved or set of complex information to be acted upon. One implication of this is that a sequence of unstructured or moderately structured interviews with an expert will result in new information being elicited in each interview but at a decreasing rate ( Hoffman, 1987, 1989). A second implication is that the knowledge extracted from the expert will depend on the type of stimuli, problems, or circumstances he or she must react to. There is not much empirical evidence available, but we assume that when presented the same highly structured situation on two different occasions, the expert will respond in the same way. Third, because knowledge elicitation seems dependent on what information is presented to the expert, more pains should be taken by the knowledge engineer in defining the range of any domain of expertise so that representative problems from all areas of the domain can be presented to the expert. Otherwise, representation of expert knowledge may remain incomplete.
Many interesting questions remain with regard to expert knowledge, both declarative and procedural, such as how this information is represented and organized in memory, and how this information is utilized. An expert can be faced with tasks of different levels of specificity, ranging from solving a specific problem to responding to the statement, "Tell me all that you know." It seems that expert knowledge is not particularly well organized in memory in the absence of imposed multiple constraints. Perhaps expert knowledge in most domains is too vast for good memory organization. The constraints imposed on the expert are what create the organization of expert information in memory and precipitate its retrieval. Herbert Simon ( 1981, chap. 3) discusses the complexity of an ant's progress across the beach and makes the point that the complexity is in the external constraints imposed on the ant, not in the ant itself. The expert is like the ant only in that he or she is used to working with the many constraints that act as memory cues, and these are what organize the expert's knowledge in memory. Unless we test the expert in a similar situation, we cannot expect to obtain highly organized performance.
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