Expert Systems are well established.
They work, and have been doing useful work since the 1980s.
Does anyone want to try to define Expert Systems?
We could do with a page on them, because unlike some other areas of AI, Expert Systems are an established technology, and its possible to write one that works.
Writing one is less difficult that writing a NeuralNet? that has some useful purpose, for example.
More about Expert Systems is needed here.
One type of Expert System uses CaseBasedReasoning?. This is a new feature used in some new expert systems.
Essentially, an Expert System that uses CaseBasedReasoning? is one that can learn from experience. It can use data that it has been given on previous occasions to tell what is happening at the present ocassion. (A normal expert system only learns what it is explicitly told.)