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Unit 13: Expert Systems and its Architecture

Choice (2) has the disadvantages: Programming skills in these languages are not common. It Notes
may be necessary to hire specialist programmers, or retrain the programming staff.
Programming the system will always be a larger (and hence longer and more expensive) task
than using a shell. Choice (3) has been the most frequent choice for commercial systems in recent
years. You will remember that an expert system shell is a ready-made expert system, with the
knowledge base missing, together with instructions for building a knowledge base in the
customer’s chosen domain.

Figure 13.3: Idea of ES Shell

Figure 13.4: Idea of ES Shell 2

13.7.1 Shells

Some organisations avoid using shells for building complete expert systems; but even they
frequently use them for:
 Training
 Building prototypes

13.7.2 Expert System Programming Environments

1. Some people make a distinction between ES shells and ES programming environments
(or “hybrid systems”). For instance, Efraim Turban does in his book (Turban, 1992).
2. Historically, this has been important because, in the 1980s, most expert systems projects in
the UK used shells, and most expert systems projects in the USA used environments.
3. Environments were so called because they provided several different forms of knowledge
representation, for instance,

(a) rules
(b) metarules
(c) frames
(d) semantic nets

4. Several different forms of inference, e.g.
(a) forward chaining
(b) backward chaining
(c) bidirectional chaining

(d) non-monotonic reasoning

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