CS322, Fall 1997 - Solution to Midterm Exam -- Solution to question 3(a)(ii)

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Solution to question 3(a)(ii)

Is the arc <Y,X> arc consistent?

Arc <Y,X> is arc consistent means that for every Y there exists an X such that r(X,Y) is true.

Note that the relation r(X,Y) corresponds to two arcs, <X,Y> and <Y,X>. You do not swap the arguments to r(X,Y). (This was the most common mistake).

The following table shows for each value of Y a value of X such that R(X,Y) is true:

Y X

a b

d a

i d

r a

Thus the arc <Y,X> is arc consistent.