People who write expert systems often need to update the knowledge bases to reflect changes in their subject. There are now a number of commercially available expert systems for giving advice on tax - how to get the best relief on your mortgage, how to minimise corporation tax, and so on - and at least one experimental system for advising on Social Security benefits, though the Government seems to have decided not to make the latter generally available to claimants. Such systems have to be modified yearly to keep up with the annual amendments to income tax and decreases in benefits. In other cases, changes are needed because our knowledge, or the way we expressed it in rules, was incorrect and needs modifying. This is often the case with systems for treating electronics faults, for instance. This section puts you in the place of an expert systems programmer.
As it stands, the meaning of good fitness is rather optimistic. It would be more sensible to say that at least 50 pressups are needed. Change the knowledge base to reflect this.
Also, we would get finer gradation with a new fitness level: medium. So let's say now that someone who can do at least 25 pressups is medium fit. If they can't do that many, they're still of poor fitness. Make such a change.
Now, let's have two new ratings together with beginner and advanced: pro and semi-skilled.
Pro is better than advanced. Obviously, someone can be a pro only with a fitness level of good. And every pro must not only have good fitness, but also have taken at least 70 skiing lessons.
We shall downgrade the meaning of beginner. Now, we shall say that everyone is a beginner if they have taken nine or fewer lessons. A skier who has taken up to 20 lessons is also a beginner if his (or her) fitness is poor; but counts as semi-skilled if of medium (or good) fitness. With 20 lessons or above, any person whose fitness is poor is still a beginner no matter how many lessons they have had. Likewise, a skier of medium fitness is semi-skilled, regardless of the number of lessons.
Actually, you are also only semi-skilled even up to 40 lessons, even if your fitness is good. But should you have had 40 or more, you count as advanced.
Now, add new facts (replacing existing ones if necessary) so they correctly reflect these regulations. Test what you've done by adding facts as you did for Eddie and Charles, and asking questions about rating.
Note that Prolog can't find resorts for the new ratings. This is not surprising, as there are no facts covering them. Think of some new resorts, and add them to your knowledge base.