SQL Transactions Exercises Perform the test for the non-additive join property (

Question

SQL Transactions Exercises

Perform the test for the non-additive join property (lossless join) for the relation R(A1, A2, A3, A4, A5), and the decompositions Da, Db, Dc, Dd and set of functional dependencies F given below. Ignore attributes that are not mentioned in each subsection (e.g., you can ignore absence of A4 in Dd, test the join between R1 and R2):

Da = { R1(A1, A2) , R2(A3, A4, A5) }

Db = { R1(A3, A4) , R2(A4, A5) }

Dc = { R1(A1, A5) , R2(A4, A5) }

Dd = { R1(A1, A2, A3) , R2(A1, A2, A5) }

F = { A1 ->A4 , A4->A5   , A3->A4 }

Does the decomposition Da have the non-additive join property? Explain why or why not.

Does the decomposition Db have the non-additive join property? Explain why or why not.

Does the decomposition Dc have the non-additive join property? Explain why or why not.

Does the decomposition Dd have the non-additive join property? Explain why or why not.

Explanation / Answer

Here is the actual definition of lossless join decomposition(non-additive join) -

https://en.wikipedia.org/wiki/Lossless-Join_Decomposition

In simple words, it means after the decompositions, with the keys we have we should be able to get all the keys present in the original relation

a.For Da, R1 intersection R2 is null, which doesnt give us any functional dependencies, hence its NOT lossless

b.For Db, R1 intersection R2 is A4, with A4 we cannot derive the dependency A1-A4, hence its NOT lossless

c.For Dc, R1 intersection R2 is A5, withA5 we cannot derive A3 at all, hence NOT lossless

d.For Dd, R1 intersection R2 is A1,A2, withA1 we can get A4, with A4 we can get A5, in R1 we have A1->A3 and A1->A2 as its A1,A2,A3 there by we can get all dependencies hence it IS lossless.

Let me know if you have any questions.

Related Questions

Navigate

• Browse (All)
• Browse S
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.