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Winexsys #1

Yeni HerdiyeniComputational Intelligence LabDept of Computer Science, IPBMarch, 2007

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ExampleSuppose we are developing an expert system to supply medical advice over the telephone when the doctor is out.Assume calls are answered by non-medical personnel who run the expert system and talk with the caller. Naturally, such an expert system would need to know that if someone is sick and calls after hours, he should take an aspirin and call back in the morning.

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WinexsysQualifiers are multiple choice lists. These are typically text and can contain up to 30 values. A qualifier condition is a statement in the tree (or rule) made up of the starting qualifier text and one or more of the associated values. Qualifiers can be used in the IF part of a tree branch to test a value or in the THEN part to assign a value.

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Winexsys (2)Choices are the goals that the expert system will decide among.Depending on the Confidence Mode used, a choice may be assigned a confidence value to determine its relative likelihood. Choices can be used in the THEN part of branches only.

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Confidence Mode

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Confidence Mode

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Confidence Mode

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Confidence Mode

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Confidence Mode

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Threshold

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Backward ChainingMost expert-system problems should be divided into several subproblems which can often be divided yet again. Writing these small sets of rules to solve the smaller problems or define sub-goals is much easier. Then writing more general rules using the solutions to the smaller problems to solve the large problem can be written.EXSYS Professional tries to solve the larger problems by using the solutions to the smaller problems to derive the information it needs. Professional's ability to automatically invoke the rules needed to derive information is called "backward chaining."

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Backward Chaining (2)Backward chaining is one of the most powerful aspects of an expert system. Regardless of how the problem is approached, backward chaining will likely be used to obtain information from other rules. If programming languages are familiar, the implementation of backward chaining may seem strange because the program does so much of the work. The expert system does not have to be instructed that rules are available that allow the information to be derived or to tell the program which rules to use. If such rules exist, the program will find them and use them. Their order does not matter. If a new rule relevant to part of the decision process is needed, it can be added anywhere in the rule set.

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Rules (1)

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Rules (2)

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Rules (3)

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Rules (4)

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Rules (5)

Winexsys #1ExampleWinexsysWinexsys (2)Confidence ModeConfidence ModeConfidence ModeConfidence ModeConfidence ModeThresholdBackward ChainingBackward Chaining (2)Rules (1)Rules (2)Rules (3)Rules (4)Rules (5)