Test by Bikram | Databases | Test 1 | Question: 16

Question

The FD $A \rightarrow B, \ \  DB \rightarrow C$ implies

• A. $DA \rightarrow C$
• B. $A \rightarrow C$
• C. $B \rightarrow A$
• D. $DB \rightarrow A$

Comments

Pseudo transitive rule says A)

Answer 1

$A \rightarrow B$ i.e. B can be determined by A.

$DB \rightarrow C$ i.e. C can be determined by (D, B)

From this we can infer that (D, A) can determine C, i.e. $DA \rightarrow C$.

Proof using Armstrong's Axioms:-

$A \rightarrow B$

$DA \rightarrow DB$ (augmentation)

$DA \rightarrow C$ (transitivity)