Question 31

Definition: In a relational schema, a superkey is any set of attributes that contains a candidate key (or the primary key) as a subset.

The primary key of the schema is given as $VY$. Therefore, any attribute set $K$ is a superkey if and only if:

Check each candidate set:

• (A) $VXYZ$: contains $V$ and $Y$ (is a superkey)
• (B) $VWXZ$: contains $V$ but lacks $Y$ (NOT a superkey)
• (C) $VWXY$: contains $V$ and $Y$ (is a superkey)
• (D) $VWXYZ$: contains $V$ and $Y$ (is a superkey)

Therefore, $VWXZ$ is NOT a superkey.