Consider the following Relation R(ABCDEFH) and following dependencies set {A → B, AB → CD, C → E , D → F}. The given relation is decomposed into R1(ABC) and R2(ADEF)
(A) Lossless join and dependency preserving decomposition.
(B) Lossy join but dependency preserving decomposition
(C) Lossless join but not dependency preserving decomposition
(D) Lossy join and not dependency preserving decomposition


Answer: (D)

Explanation: Since either decomposed relations R1 or R2 not contains attribute H, which is part of original relation.
So, given decomposition is lossy join.

Now dependency preserving will be checked:
In R1(ABC)
[A]+ = ABC
In R2(ADEF)
[A]+ = NULL
[D]+ = F
[E]+ = NULL
[F]+ = NULL
Because of decomposition AB → D, C → E, is lost.
So, it is not the dependency preserving decomposition.

Option (D) is correct.

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  • Last Updated : 29 Nov, 2018

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