RULE-BASED SYSTEMS EXERCISES ANSWER SHEET
Exercise 1: SIMULATING THE INFERENCE ENGINE
A) Run the system by hand, following the procedure outlined above.
Show what happens by drawing the tree of rules, by augmenting
Worksheet 1 and indicating the dialog that would occur and the
additions to the database by augmenting Worksheet 2
Use the following data:
1. The user is 42 years old
2. has health and life insurance
3. has current savings balance of $20000
4. has a monthly salary of $3000
5. not covered by a pension plan, does have IRA
6. has one child, age 12, who does not have scholarship or a trust
fund, is not eligible for a loan, and would like to attend a school
with expensive tuition
7. does not currently own a house and would like to.
WORKSHEET 1
WORKSHEET 2
DIALOG DATABASE
Attribute Value Source
1) Do you have health insurance?
** YES HaveHealthInsurance Yes user, quest. 1
B) How would the program respond if, in answer to the question "do you
have an pension", you had answered "WHY"?
(Hint: recall the mechanism used for explanation)
Do you have a pension?
** WHY
C) How would the program respond to the question shown below?
(Hint: recall that the system displays the "audit trail" of the rules
used to reach that conclusion, i.e., all the rules that lead to that
specific answer.)
HOW DID YOU DECIDE THAT THE INVESTMENT SHOULD BE CONSERVATIVE GROWTH?
D) How would the program respond to the question
HOW DID YOU DECIDE THAT THE INVESTMENT SHOULD BE GROWTH AND INCOME?
Exercise 2: DEALING WITH UNCERTAIN RULES
A) Using the scheme outlined above, what would be the resulting degree
of belief from the following sequence of rules (assume all are
relevant, and note that some certainties are negative):
I) If ... then investment should be G&I .6
II) If ... then investment should be G&I -.2
III) If ... then investment should be G&I .8
IV) If ... then investment should be G&I -.45
(B) What happens if the rules fire in the order (IV) (II), (III), (I)?
Does this seem intuitively reasonable? Why, or why not?
C) What would the strength of conclusion be if the user had answered .9?
D) Work through the certainties that would be computed by the three
rules below.
(Note that this example exercises all of the machinery we need for
certainties. We have abbreviated the premises and conclusions to
single letters, to simplify things and focus on the issue of modeling
uncertainty.)
(I) If A and B then E .7
(II) If C or D then not E .45 (i.e., E with a certainty of -.45)
(III) If E then X .8
Assume that the user answers the questions as follows:
A?
** YES .8
B?
** YES .9
C?
** YES .9
D?
** YES .5
How strongly do we now believe X?
E) Work through the certainties that result from the following four
rules, assuming that the user's answers to F, G, H, J, and K are all
YES with certainty 1.0.
(I) If F then Y .7
(II) If G then Y .8
(III) If H then Y .5
(IV) If J then Y .6
What is the strength of belief in Y at this point?
Imagine that we had the two additional rules (V) and (VI) shown below
and that they fired. Would we be absolutely certain in our belief in
Y?
(V) If J1 then Y .7
(VI) If J2 then Y .8
Now imagine that rule (VII) fires. Now how strong is our belief in Y?
(VII) If K then Y 1.0
What does this demonstrate about the strength of belief accumulating function?
Exercise 3: RULES ARE SUPPOSED TO CAPTURE THE LOGIC OF THE SITUATION
A) As in Exercise 1, show the dialog would result from traversing this
tree and the additions to the database that would result. Use the
degree of certainty machinery we just reviewed.
Note that you have far less work to do on this problem because we have
given you the entire tree. You only have to traverse it, and show the
dialog and conclusions.
The user
1. is 70 years old
2. does not have health insurance
3. does have life insurance
4. has a current savings balance of $20000
5. has a monthly salary of $3000
6. is covered by a pension plan
7. has no children
8. currently owns a home
What is the system's recommendation?
WORKSHEET 3
DIALOG DATABASE
Attribute Value Source
B) Now suppose rule 10 were moved down the page to the end of the list
of rules concluding about fund category (i.e., after rule 22).
Describe what difference this makes in the trace of the reasoning
process and in the dialog. Also, does this change the final result?
(As in earlier exercises, this should not require a great deal of work
if you think carefully and rely on what you did in the previous part
of this exercise.)
Exercise 4: KNOWLEDGE ACQUISITION
A) Try writing two rules to help out. Do this by filling in the blanks
below. Use anything you know that is a good plausible guess. Remember
that we're trying to come up with good guesses here, not absolute,
hard and fast answers.
If ___________________
then the tuition is likely to be EXPENSIVE.
If ___________________
then the tuition is likely to be CHEAP.
B) Why is it true that we need look at only this one part of the tree?
We added rules 60 and 61 to the knowledge base, and gave no further
guidance, yet without re-running the whole example we can say with
assurance that the only thing that changes is the system's behavior
when the issue of tuition level arises. Why is this so?
C) Using the hints above, show the revised sub-tree of rules that
result and show the parts of the dialog that differ from the example
of Exercise 1.
D) If the rules you made up in part (a) were different from those
shown in part (b), add those rules to the knowledge base and show how
the consultation will change. If they were the same as the ones shown
in (b), write two new ones, add them to the knowledge base, and repeat
exercise (c) using your revised knowledge base. (Show below the
revised sub-tree and the parts of the dialog that change.)
Exercise 5: ASKING VS. INFERRING
A) Run the same example as in Exercise 1, knowing the additional facts
that: The College Category is OUT-OF-STATE (i.e., neither IVY-LEAGUE
nor IN-STATE) the College Setting is SMALL-TOWN (i.e., neither RURAL
nor URBAN) the college is not competitive, not famous, and doesn't
have a prestigious faculty the College Tuition Level is CHEAP (i.e.,
you do in fact know the tuition level).
Use the same hints as in Exercise 4, namely, use the simple inference
engine and note that once again we simply have a new subset of rules
added at one part of the tree. You don't need to re-do the entire
tree.
Show the part of the reasoning tree that has changed, and the new
questions that result in the dialog.
B) Do the example above again, this time as it would appear if
Tuition is marked as "ask first". As before, all you need concentrate
on is the part of the tree and dialog that changes. Show how the
revised part of the reasoning tree would look and how the dialog would
change.
C) How does the dialog change if the user responds "unknown" to the
question "What is the college tuition level?" Show the sub-tree and
dialog one last time.
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