3 votes 3 votes Databases database-normalization + – Shefali asked Oct 10, 2015 Shefali 1.7k views answer comment Share Follow See all 0 reply Please log in or register to add a comment.
0 votes 0 votes I think we can decompose to BCNF but it will violate the dependency preserving. Here AC is the candidate key BCNF decomposition R1(ABC) (AC is the candidate key ) R2(BCD) (BC+ is the candidate key) R3(DE) ( D+=DE D is the candidate key) AC->BC BC->D D->E Further no decomposition is possible ! I guess. So option B Umang Raman answered Oct 10, 2015 Umang Raman comment Share Follow See all 14 Comments See all 14 14 Comments reply Arjun commented Oct 10, 2015 reply Follow Share Why ABC and not just AB? 0 votes 0 votes Umang Raman commented Oct 10, 2015 reply Follow Share if i keep only AB then B will be referred so for B+ we have to check for candidate key for its set which is not! is it right way? i am confused now! 0 votes 0 votes Arjun commented Oct 10, 2015 reply Follow Share yes, you are correct. Common attribute B is not the candidate key and hence decomposition will become lossy. 0 votes 0 votes Aditya commented Oct 10, 2015 reply Follow Share what about (ACD,DE,AB) ?? 0 votes 0 votes minal commented Oct 16, 2015 reply Follow Share is there any problem with AB,DE,BCD,AC ..it is after 3nf and it is also in bcnf ... and dependency preserve also ...? 2 votes 2 votes Arjun commented Oct 16, 2015 reply Follow Share Yes, both the above satisfies BCNF and are dependency preserving. it is advised to follow the BCNF decomposition algorithm - otherwise mistakes might happen. 0 votes 0 votes minal commented Oct 16, 2015 reply Follow Share AB,BCDE,AC AFTER 2NF decomposition , AB,BCD,DE,AC after 3nf decomposition ...so ans is A) 2 votes 2 votes vineet.ildm commented Sep 23, 2017 reply Follow Share @arjun sir please tell what is the final answer whether it is dependency preserving or not. i have used proper bcnf decomposition algorithm and got these decompositions: (A,B),(D,E) and (A,C,D) and with these dependency is not preserved. 0 votes 0 votes Arjun commented Sep 23, 2017 reply Follow Share @vineet Now apply dependency checking algorithm on those. What answer do you get? 0 votes 0 votes vineet.ildm commented Sep 23, 2017 reply Follow Share Plz check this 0 votes 0 votes vineet.ildm commented Sep 23, 2017 reply Follow Share @arjun sir i have checked that too not getting BC->D 0 votes 0 votes vineet.ildm commented Sep 23, 2017 reply Follow Share @arjun sir after directly applying bcnf decomposition algorithm for this question we will not get dependency preservation. but 3nf decomposition gives decompositions which are also in bcnf. so if we get bcnf decompositions from 3nf decomposition can we answer yes for such question? 0 votes 0 votes Arjun commented Sep 23, 2017 reply Follow Share No, In your decomposition, you get AC->D, FD and also A->B. And when you take closure, this covers BC->D. So, it is dependency preserving -- you might be applying the dependency check wrongly. 0 votes 0 votes jiminpark commented Jan 13, 2022 reply Follow Share @vineet.ildm Sir , I am getting the same decomposition as yours. So is it wrong? @Arjun Sir, please tell if it will dependancy preserving / not ? because the 3NF form decomposition is also lossless. 0 votes 0 votes Please log in or register to add a comment.
0 votes 0 votes Ans should be yes..!! R1(A,B) R2(A,C) R3(B,C,D) R4(D,E) rishu_darkshadow answered Sep 21, 2017 rishu_darkshadow comment Share Follow See all 0 reply Please log in or register to add a comment.
0 votes 0 votes Answer is option b: NO Cannot decompose into BCNF without violating Functional Dependency Preservation. Varun Raj Akula answered Jan 22, 2022 Varun Raj Akula comment Share Follow See all 0 reply Please log in or register to add a comment.