1. Consider the following set of known facts and rules for a production system.
ID: 3728411 • Letter: 1
Question
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?
Explanation / Answer
Hi,
Forward chaining is a technique in which the inferences are made based on the given facts and using them against the rules, like a bottom up approach.
For example in this case, given the facts are L,M,N are true.
Now, we go through each rule to get inferences
In first iteration:
rule 1 will be fired, since L is true and we get decision as O is also true
rule 2 will also be fired, since M and N both are true and the decision taken is Q is true
rule 3 will be fired as N is true, decision being R is also true
rule 4 will not be fired, since P is not known
rule 5 will be fired since R is true, decision is U is true
rule 6 will not be fired as no info in P
rule 7 also will not be fired as no info on T
rule 8 not fired because no info on S
rue 9 fired because O is true and decides T is true
rule 10 is fired since M and N are true and decides P is true
rule 11 not fired since no info on X
Now again in second iteration,
same firing for rules that have been fired, so lets look at what happens to the not fired ones from iteration 1
rule 4 will now be fired since P and Q are true, decides S is true
rule 6 will now be fired, since we now know P is true, decides W is true
rule 7 will now be fired, decides Z is true
rule 8 fired since S and U are true, decides V is true
rule 11 not fired since no info on X
so by the end, we know that all rules have been fired excep for rule 11
and we know that L,M,N,O,Q,R,U,T,P,S,W,Z,V are true.
Thumbs up if this was helpful, otherwise let me know in comments.
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