Most expert systems have explanation facilities that allow the user to ask questions - why and how it reached some conclusion.
The questions are answered by referring to the system goals, the rules being used, and existing problem solving. The rules typically reflect empirical, or "compiled" knowledge. They are codes of an expert's rules of thumb, not the expert's deeper understanding.
Dialog with an expert system designed to give advice on car problems.
System Does the car start ?
System Does the engine turn over ?
System Do you smell gas ?
System Recommendation - Wait 5 minutes and try again.
User Why ?
System I used the rule:
If not start, and engine_turn_over, and smell_gas
Then recommendation is 'Wait 5 minutes and try again'
Note : The rule gives the correct advice for a flooded car, and knows the questions to be ask to determine if the car is flooded, but it does not contain the knowledge of what a flooded car is and why waiting will help.
Types of Explanation
There are four types of explanations commonly used in expert systems.
Rule trace reports on the progress of a consultation;
‡ Explanation of how the system reached to the given conclusion;
‡ Explanation of why the system did not give any conclusion.
Explanation of why the system is asking a question;
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