NIELIT Scientific Assistant A 2020 November: 72

Question

Let $\text{R=(A,B,C,D,E)}$ having following $\text{FDs}.\;\text{F}=\{\text{A}\rightarrow \text{BC, CD} \rightarrow \text{E, B}\rightarrow \text{D, E}\rightarrow \text{A}\}.$

Which of the following is not a Candidate key?

• A. $\text{A}$
• B. $\text{B}$
• C. $\text{E}$
• D. $\text{BC}$

Answer 1

In a given relation a key is a candidate key if it’s able to identify all tuples uniquely,(minimal set of attributes.

$R(A,B,C,D,E)$

$FD’S:A \rightarrow B,CD\rightarrow E,B\rightarrow D,E\rightarrow A$

clouser of $A^+=ABCDE$

clouser of $B^+=BD$

clouser of $E^+=ABCDE$

clouser of $BC^+=ABCDE$

here B is not able to identify all the tuples in the given relation. so B is not candidate key.