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2.2. SINGLE VS. MULTIPLE EXPERTSAn expert system development project may utilize one expert or a number of them as the primary source of domain expertise. The use of a single expert is sometimes preferred, but there are many cases in which it is useful or necessary to utilize multiple experts. There are four primary problems with knowledge acquisition from a single expert: (1) difficulty in allocating adequate time by a key individual in the organization, that may create a bottleneck in the expert system development process; (2) personal bias, that may affect the performance of the system; (3) limitation to a single line of reasoning, that may affect the usefulness of a system, since expert systems that are developed based on a single, perhaps narrow, line of reasoning do not emulate most real-life decision making; and (4) incomplete domain expertise, that may affect the performance of a system (McGraw and Harbison-Briggs, 1989). The first problem may create a bottleneck in the expert system development process. If only one expert is the sole knowledge source for the expert system, it is very difficult to acquire a sufficient amount of his or her time. This is not because of an unwillingness to cooperate with the knowledge engineer, but because of other commitments and the fact that knowledge acquisition is so time-consuming. Depending upon the availability of such an individual can delay a project's progress. Personal bias, which constitutes the second problem, may affect the performance of the system. The third problem affects the usefulness of a system, since expert systems that are developed based on a single, perhaps narrow, line of reasoning do not emulate most real-life decision making. Furthermore, with attempts to apply expert systems technology to more sophisticated problems, restricting the knowledge acquisition activity to a single expert could result in incompleteness of the system. Experts by definition are "very knowledgeable about only a small subset of the tasks in the domain." As expert systems become more and more complicated and the domains become more complex, the required expertise is most likely to reside in not one but a team of experts. A designated primary expert is needed when multiple experts are utilized (Prerau, 1990). Incorporating the expertise of a team of experts provides the following positive effects on the resulting expert system: (1) it assures that the knowledge base can be complete; (2) it improves the likelihood of obtaining specialized knowledge in subdomains of the problem; (3) it increases the quality (i.e., reliability and consensus among experts) of the acquired knowledge; (4) it assures that the facts that are included in the knowledge base are important ones; (5) it enhances understanding of the domain knowledge through discussion, debate, and exchange of hypotheses between members of the expert team; and (6) it encourages interactions among experts and creates a synergy such that the acquired group knowledge is greater than the sum of the individual's knowledge. When multiple experts are involved in the development process, knowledge acquisition sessions can be flexibly designed. First, it is not necessary that all experts be present at the same time in one place throughout the acquisition process. Advanced information technology such as group support systems can be used to facilitate interactions with experts, not only in face-to-face meetings but also in meetings conducted in dispersed locations. Second, interactions among experts can create a synergy such that the acquired group knowledge is greater than the sum of the individual's knowledge (Liou, Weber, and Nunamaker, 1990). However, the involvement of multiple experts increases the complexity of the knowledge acquisition process and makes an already difficult task even more complicated. Two factors contribute to this complexity. One factor involves the difficulty of merging each individual expert's knowledge structures into one group knowledge structure that provides the underlying problem-solving expertise of the expert system. This involves resolving conflicts between various problem-solving approaches and reasoning processes. The other factor involves the difficulty of the generation of group knowledge that does not reside in any one individual expert but evolves as a result of the group interaction. A group support system has been proven to be useful and effective to ease these difficulties when acquiring knowledge from multiple experts (Liou, 1992). 2.3. ROLE OF KNOWLEDGE ENGINEER, END-USERS, AND MANAGERSA knowledge engineer is the individual responsible for structuring and constructing an expert system. The literature reveals diverse perspectives on the qualifications and responsibilities of the knowledge engineers, that include leading and managing the project, defining the problem domain, selecting hardware/software, acquiring and representing knowledge, implementing the expert system, interacting with users and managers, preparing technical documentation, verifying and validating the system, training users, operating and maintaining the initial system, and providing advice for further extension and updates (Prerau, 1990). Knowledge engineers should have some mastery of the domain to identify the type of knowledge that is required. They should be able to conceptualize and analyze the problem, to employ various knowledge acquisition techniques, and to communicate and work with other people. Users and managers should be involved in the knowledge acquisition task, especially in the planning stage where decisions of problem scope are made and in the verification stage where the prototype system is evaluated. The problem scope should be jointly determined by a group of people that includes domain experts, users, managers, and knowledge engineers. Domain experts provide a subjective perspective of what the system can do for users, while users provide a broader perspective of how the system may be able to help them. Managers provide strategic guidelines as to what should and should not be included in the system. Knowledge engineers can assess technical feasibility. One individual, such as the manager, can of course decide the scope of the system based on policies and the needs of the organization. However, systems that involve users in the development process tend to be more acceptable to the users when they are delivered.
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