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Lossless Decomposition in DBMS
  • Difficulty Level : Hard
  • Last Updated : 20 Aug, 2019

Decomposition of a relation R into R1 and R2 is a lossless-join decomposition if at least one of the following functional dependencies are in F+ (Closure of functional dependencies)

R1 ∩ R2 → R1
R1 ∩ R2 → R2

Question 1:
Let R (A, B, C, D) be a relational schema with the following functional dependencies:

A → B, B → C,
C → D and D → B. 

The decomposition of R into 
(A, B), (B, C), (B, D)

(A) gives a lossless join, and is dependency preserving
(B) gives a lossless join, but is not dependency preserving
(C) does not give a lossless join, but is dependency preserving
(D) does not give a lossless join and is not dependency preserving

Refer this for solution.

Question 2
R(A,B,C,D) is a relation. Which of the following does not have a lossless join, dependency preserving BCNF decomposition?
(A) A->B, B->CD
(B) A->B, B->C, C->D
(C) AB->C, C->AD
(D) A ->BCD

Refer this for solution.

Below is the Quiz of previous year GATE Questions

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above

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