15. A 3NF decomposition of the relation in Problem 14 is AB and BCD ABC and CD A

Question

15. A 3NF decomposition of the relation in Problem 14 is AB and BCD ABC and CD AC and BCD ABD and BC. a. C. b. d. 16. R(A, B, C, D) has FD's A->B, BC->D, and D->A. Which FD does not follow from the given FD's? a. AC->D c. BD->C b. BC->A d. CD->B 17. What is not a key to the relation in Problem 16? a. AB b. BC C. CA d. CD 18. The relation in Problem 16 has been projected onto relation S(B, D). Which FD's holds in S? a. B->D b. BC->D c. BD->A d. D->B 19. The assumption that a course is taught uniquely for each student by a professor is represented by the functional dependency a. professor->(course, student) b. (course, student->professor. c. (course, professor->student. d. (student, professor)->course

Explanation / Answer

15) The Fourteen question is not given above if you can then post it in comments

16) Answer is C

because using B and D we can derive A but not C

17) Answer is A

because take AB in this A can derive B then B alone can not derive any other column of a relation.A key must derive all the columns of a relation

take option B: CA in this A can derive B now we have CAB from this C and B both together derive D which is BC->D and now we have all the columns of relation.The other 2 options C and D will also become keys

18) Answer is C

because individually D can derive A so BD->A, FD holds

19)C is the answer

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