2 votes 2 votes Databases gateforum-test-series databases lossless-join bcnf-decomposition + – Mk Utkarsh asked Jan 12, 2018 Mk Utkarsh 1.5k views answer comment Share Follow See all 34 Comments See all 34 34 Comments reply Show 31 previous comments Mk Utkarsh commented Jan 12, 2018 reply Follow Share 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 0 votes 0 votes Higgs commented Jan 12, 2018 reply Follow Share I think I need to revisit my concepts. Thanks everyone. Future comments are welcome. 1 votes 1 votes Higgs commented Jan 19, 2018 reply Follow Share 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. 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. Thankyou @joshi_nitish, @Hemant, @Mk. 2 votes 2 votes Please log in or register to add a comment.
0 votes 0 votes Answer must be 'A'.... As in option B dependency is preserved.... Achal Gupta 1 answered Jan 12, 2018 Achal Gupta 1 comment Share Follow See all 2 Comments See all 2 2 Comments reply Nishtha3121996 commented Jan 12, 2018 reply Follow Share How is dependency preserved in second option can you please explain as from ADC decomposition AB -) C can't be derived 0 votes 0 votes Achal Gupta 1 commented Jun 26, 2018 reply Follow Share 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 0 votes 0 votes Please log in or register to add a comment.