Functional coverage

What is the relation of constraints and coverage? If I have given constraint on some variable then, is it mandatory to write coverage of it?

Constraints are used to control the range of your stimulus during randomization.

If you have given constraint on a Variable, you can write the coverage on its possible valid values given by the constraint condition.

Hence, the coverage is being written for the Variable and not the constraint.

In reply to nitishg:

So is it mandatory to cover those variables?