Gateforum DBMS

Question

Comments

i don't think we have to use JOIN specifically just need to do union of FD's. like from SQL viewpoint we can use AB and uniquely identify C right? it doesn't matter if tables are different because B-->D and D--->B

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I think I need to revisit my concepts. Thanks everyone.

Future comments are welcome.

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Update: If you are reading this discussion then please note that what others have pointed out is absolutely correct.

i.e. dependencies are preserved in both decompositions.

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Actually, I was simply checking whether $F_{1}^+ \ U\  F_{2}^+ = F^{+}\ or\ not.$

But the correct approach is $(F_{1}^+ \ U\  F_{2}^+) ^{+}= F^{+}$

i.e. We take the union of F1 and F2  and then keen closure.

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Thankyou @joshi_nitish, @Hemant, @Mk.

Answer 1

Answer must be 'A'.... As in option B dependency is preserved....

Comments

How is dependency preserved in second option can you please explain as  from ADC decomposition AB -) C can't be derived

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In this we have to check whether the dependency is preserved or not for decomposition ADC..... So take the dependency AB - >C and check using polynomial time algorithm ( it is an algo used to find out whether dependency is preserved or not...)..... Then u will get your answer