This book concentrates primarily on the techniques used by the system engineer and knowledge engineer to design customized systems. It explains the various types of inference engines and knowledge bases that can be designed, and how to build and use them. It tells how they can be mixed together for some problems, and customized to meet the needs of a given application. There are a number of features which are commonly used in expert systems. Some shells provide most of these features, and others just a few.
Customized shells provide the features which are best suited for the particular problem.
That is, the aim of the system is to pick the best choice from many enumerated possibilities. For example, an identification problem falls in this category. Diagnostic systems also fit this model, since the aim of the system is to pick the correct diagnosis. The knowledge is structured in rules which describe how each of the possibilities might be selected. The rule breaks the problem into sub-problems.