1. Consider the following set of known facts and rules for a production system. (Check the Forward and Backward Chaining slides in the Rule-Based Systems file in Module 3 for an example).

Facts (known to be true): L, M, N

Rules: 1. L O (means that if L is true then O is true)

2. M & N Q (means that if M and N are both true then Q is true)

3. N R

4. P & Q S

5. R U

6. P W

7. T & W Z

8. S & U V

9. O T

10. M & O P

11. R & X Y

a. Which rules would fire and in what order if we used forward chaining, assuming the system starts at rule 1 and goes to rule 11 and repeats. What facts do we know after forward chaining has completed?

b. Using backward chaining, prove that Z is true. Which rules and in what order, would fire to accomplish this? What facts do we know after backward chaining has completed?

c. Using this example, what have we learned about the applications for forward and backward chaining? Give an example of a situation where each would be the best choice.