selft doubt

Question

can we consider  , proper subset of candidate key union proper subset of another candidate key

as a proper subset of candidate key.

Answer 1

Consider the relation scheme R(A, B, C, D, E, H) and the set of functional dependencies-

A → B

BC → D

E → C

D → A

• Determine all essential attributes of the given relation.
• Essential attributes of the relation are- E and H.
• So, attributes E and H will definitely be a part of every candidate key.

So candidate keys are AEH, BEH, and DEH. 
 

Now, we can see A is proper subset of AEH. 

And B is proper subset of BEH (another candidate key). 
 

A union B is AB, which is not a proper subset of any candidate key. So, we can’t consider the given statement to be true.