Domain of Attributes for an Entity?
I found my answer from the book &quot;Database system concepts&quot;. Here's what that means:
Suppose C is a composite attribute of an entity type, which has 3 attributes : A1, A2, A3. Suppose, only A3 is multivalued.
Now say the domain of these 3 attributes contain 5, 4, 3 elements respectively.

The domain of Multi-valued attributes is a set of subsets of values
from the basic domain.

This means, the multi-valued attribute's (A3 in our case) domain will be the Power set of the basic domain set.
So, in our case, the power set of A3 will contain 2^3 = 8 elements. So, the composite attribute C will contain 5x4x8 = 160 elements.
In case A3 was not multi-valued, then the domain of C would contain 5x4x3 = 60 elements.