DBMS-Normalisation-Lossless Join Decomposition

Question

Comments

Should be A... confirm please

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I think so ..bt given ans C...

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It's A only....there will be spurious tuples. So union can never be R.

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@Shaik Masthan

Can you give a answer for this question.

Answer 1

it is option A only. point  2 will never be correct. if A is subset of B then A union B will be B only

Answer 2

Ans is option a)

Let R be the relational schema with instance r is decomposed into R_1,R2,….,Rn with instance r₁,r₂,…..,r_n. 
If r₁ ⋈ r₂ ⋈ ……. ⋈ r_n ⊃ r , then it is called Lossy Join Decomposition.

i.e. if the original relation is the proper subset of natural joins of all the decompositions, then it is said to be Lossy Join Decomposition.

Answer 3

4th is false because it result in R rather then (R1XR2)
2nd one is false as it result in R1XR2
only 1st one is true as the definition.

Answer 4

i think option C is correct one because ..

(iii) Is correct one now i am thinking about (ii)

[R1 natural join  R2] = R (Must be lossless join decomposition  in this relation by using natural join one should able to retrieve the exact record set of R   ) 

Now  [ R U { R1 natural join R2)} ] i.e not equals to exact record set R so it is not lossless join.

please correct me may be my approach is wrong