5.5. A PRACTICAL EXAMPLE
5.5.3
73
Implementation and testing
The Coins of Upper Scholaria Using an expert system shell available to you, create a "Coins of Upper Scholaria" knowledge base. Check whether your chosen expert system shell uses forward or backward rules (some allow you to use either). You may need to alter the syntax for the shell that you have chosen. Compile the knowledge base, and test it by consulting its user interface. Make sure that:
¯ it correctly identifies each of the coins; ¯ it reports "no solution" if you describe a coin which does not exist (e.g.
a silver
coin, 22mm in size, which is seven-sided and has a flower on it.)
5.5.4
Justification and explanation
A human expert can not only give good advice, but can explain or justify his reasoning. This is important for several reasons:
¯ it helps the enquirer to understand the subject better; ¯ it means that the enquirer can learn how the expert thinks; ¯ it gives the enquirer more confidence in the advice given. The last of these is particularly important. Imagine an oil tycoon considering where to spend 1 billion on a new drilling exploration project. He asks his expert advisor, who answers "Try drilling at Deadman’s Gulch in Arizona". The tycoon might ask the expert to justify this suggestion. "No reason - just a hunch", says the expert. The tycoon would want more reassurance than that! If the expert could show him geological maps, the results of test drills and so on, the tycoon would be more inclined to take the advice. The same is true of Expert Systems. The user requires some justification to give confidence that the advice given by the system is based on logical reasoning, and is not just the computer’s "hunch". All expert systems provide this. The user interface has built-in functions which can explain the reasoning of the inference engine. For this reason, the user interface is often called an explanatory interface. The explanatory interface can provide two types of justification - these are why and how. Why? The why justification feature allows the user to ask the system "Why are you asking me that question?". This is useful when using an expert system to learn how the expert thinks. Why does the doctor ask you how often you drink alcohol? Why does the technician ask you if you have recently downloaded something from the internet? Why does the antique dealer ask if the furniture has been stored in a humid atmosphere? By revealing why a question is being asked, the user can gain an understanding of the line of reasoning which the system is trying to follow.
c
H ERIOT-WATT U NIVERSITY 2005
30 min