1. Consider the following set of known facts and rules for a production system.
ID: 3727792 • 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?
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.
Explanation / Answer
a)- L M N q r u O T P U W Z V
b)- L M N TRUE
L->O
O->T
M & O -> P
P -> W
T & W -> Z
c)- Chaining is a technique used in applied behavior analysis to teach individuals with developmental disabilities complex tasks by breaking them down into discrete responses or individual behaviors.[1] With a backward chaining procedure, all of the behaviors in a single task are completed by the trainer except the last step. The learner is then prompted to complete the last step in the task. Once the learner has demonstrated independence in completion of the last step, the trainer then completes all steps except the last two, prompting the learner to complete the last two steps independently. This sequence proceeds backward through the chain until all the steps in the task have been introduced in reverse order and practiced cumulatively.
In order to teach a task utilizing a backward chaining procedure, begin by breaking down the entire task into individual steps.
For example, a tooth brushing routine may be broken down as follows:
1. Apply toothpaste to toothbrush, 2. Wet toothbrush, 3. Brush top teeth, 4. Brush bottom teeth, 5. Rinse toothbrush, 6. Rinse mouth, 7. Dry mouth
The trainer would begin by completing each step for the learner beginning with step one (Applying toothpaste to the toothbrush). Once the trainer has completed all steps, the trainer allows the learner to complete the last step (Dry mouth) independently. The trainer will then move on to training the last two steps (Steps 6 and 7). This training will continue until the student is completely independent and can complete the entire tooth brushing routine without assistance. It is important to note that transitioning from one step to the next will vary from learner to learner and should not be done until the learner is proficient in the targeted step.
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