Question

Which of the following is not a condition for the third normal form in the case of XY?

(a) X→ Y is trivial

(b) X is the superkey for R

(c) Each attribute in Y-X is a candidate key for R

(d) Each attribute in X-Y is a candidate key for R

The question was asked in a national level competition.

Enquiry is from Decomposition Using Functional Dependencies in division Relational Database Design of RDBMS

Answer 1

The correct answer is (d) Each attribute in X-Y is a candidate key for R

To elaborate: Each attribute in X-Y is a candidate key for R is not a necessary condition for the third normal form in the case of X →  Y. X→Y is trivial and X is the superkey of R are necessary conditions for the third normal form.