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Question 87

Given an instance of the relation R(ABCD). A | B | C | D

Given an instance of the relation R(ABCD). A | B | C | D a₁ | b₁ | c₁ | d₁ a₁ | b₂ | c₂ | d₂ a₂ | b₂ | c₂ | d₃ a₃ | b₃ | c₄ | d₃ Which of the following functional dependencies hold?
  1. A{A B} → D and D → A
  2. B{A B → C} and B → D
  3. C{A B} → C and B → C
  4. D{A B} → D and A → D
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Correct answer: (C) {A B} → C and B → C

Explanation

AB → C holds because every (A, B) pair is unique, and B → C holds because b1→c1, b2→c2 (twice) and b3→c4. B → D fails (b2 gives d2 and d3), as do D → A and A → D.

From DSSSB TGT Computer Science Practice Set 3

This is question 87 of DSSSB TGT Computer Science Practice Set 3. See all questions of this paper with answers, or attempt the paper as a timed online test to get your score and all-India rank.