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Besides the coverage of the levels of the methodological pyramid, the scope of the methodology is another important aspect to consider. With scope is meant the range of activities included in a methodology. Building a KBS is not a one-dimensional affair; it encompasses a wide range of problems and tasks running from organizational factors to low-level coding in a programming/development language.

Based on the methodological pyramid and the scope, the approaches appearing in the literature can be placed into three general classes:

  1. Boxes-and-arrows approaches. These approaches are characterized by the fact that they are mainly limited to giving a kind of "life-cycle" consisting of boxes, denoting developing activities, and arrows linking these activities, to generate a sequence. What these approaches lack is a detailed specification of the "how" of the boxes. That is, there are no methods, techniques, or tools provided. However, they cover most of the activities normally seen as important in developing KBSs, albeit in a very general way. They are broad and shallow.
  2. Focused approaches. These limit themselves to one or a few methods and techniques that cover part of the work to be done. Within certain bounds they can be seen as "mini methodologies": in their limited scope they sometimes cover all levels of the pyramid. Being focused on a limited number of activities, they are narrow and deep.
  3. Full-fledged methodologies, providing support for all levels in the pyramid. As we shall see in Section 5, these come in two strands:
    • Methodologies for conventional systems design with "KBS oriented" additions
    • Methodologies specially designed for KBS development

    Claiming to cover all levels of the pyramid and including all important aspects of KBS development, they can be seen as broad and deep.

Before starting the survey of these classes of approaches, it must be emphasized that the methodological pyramid and the derived classification do not imply a value judgment. Though it may seem that "more is better," this cannot be proven to be true in general. From experience with methodologies for the development of conventional systems, we know that a "bad" methodology in the hands of an experienced person may turn into a "good" one, while a "good" methodology may be spoiled by the incompetence of a user. Just as shouting "faster" may sometimes help the runner, boxes-and-arrows may sometimes help the developer.

In more general terms, it is extremely difficult to judge the value of a methodology in an objective way. Experimentation is of course the proper way to do it, but is hardly feasible because there are too many conditions that cannot be controlled. Moreover, nobody will in practice pay for building the same KBS twice with different approaches. Introducing an experimental toy problem will violate the basic assumption behind the need for a methodology: a complex development process. So, of necessity, the notion of "achievement" will be limited mainly to reported use in practice. Though it could be an interesting research project, investigating the relation between use of a methodology and "success" of a KBS is outside the scope of this chapter.


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