Unit 4 · Database Management Systems Paper 2 CS · December 2019

Directions (Q96–100): An organization maintains a database with five attributes A, B, C, D, E. Consider the universal relation R(A, B, C, D, E) with functional dependency set F = {A → BC, D → E, BC → D, A → D}. All attributes are simple and atomic.

Assume that given table R is decomposed in two tables R (A, B, C) 1 with functional dependency set f = {A → B, A → C} 1 and R (A, D, E) FD 2 with set F = {A → D, D → E} 2 . Which of the following option is true w.r.t. given decomposition?

Pick an option to check yourself, or open the answer below.

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Correct answer: D. R1 is in 3NF and R2 is in 2NF

Explanation

R1(A, B, C) has only A → B, A → C, so it is in 3NF (even BCNF). R2(A, D, E) has A → D → E, a transitive dependency, so it is only in 2NF. BC → D is lost, so dependencies are not preserved.

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Assume that given table R is decomposed in two tables R (A, B, C) 1 with functional dependency set f = {A → B, A → C} 1 and R (A, D, E) FD 2 with set F = {A → D, D → E} 2 . Which of the following option is true w.r.t. given decomposition?

Explanation

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