Expert Systems vs. Decision Trees

There is a rule used by Expert Systems experts:

If:   There is a known algorithm to solve
      a problem,
Then: Use it.

So, if a decision tree will work for your problem, by all means use one.

The trouble is that decision trees work only for a relatively small class of problems, where:

1. All needed data can be obtained with certainty.
2. Data are discrete (Boolean or one of a fixed set of choices).
3. The structure of the problem is known and is fixed.
4. The problem can be ``factored'' well, preferably many times.
5. There is a single conclusion for each set of data.