1 votes 1 votes a relational schema R (A, B, C, D) is decomposed into (A, B), (B, C), (B, D). If functional dependencies A → B, B → C, C → D and D → B were present in R, is the decomposition preserving dependencies? Databases dependency-preserving databases + – sh!va asked Jan 23, 2017 sh!va 468 views answer comment Share Follow See all 0 reply Please log in or register to add a comment.
Best answer 2 votes 2 votes It is dependency preserving: Ref: https://gateoverflow.in/3371/gate2008-it-61 Given FDs are transitive. B → C, C → D = B → D. Hence keeping B → D preserves B → C and C → D similarly C → B preserves C → D and D → B R1 (A, B), gives A → B R2 (B, C) gives C → B // C → D and D → B R3 (B, D) gives B → D //Hence B → C and C → D Hence it is Dependency preserving. sh!va answered Jan 24, 2017 • selected Jan 24, 2017 by srestha sh!va comment Share Follow See all 0 reply Please log in or register to add a comment.
0 votes 0 votes functional dependency C->D is not possible in decomposed realtions R1(A,B) , R2(B,C) and R3(B,D). So decomposition is not preserving dependencies jatinkumar answered Jan 23, 2017 jatinkumar comment Share Follow See all 0 reply Please log in or register to add a comment.
0 votes 0 votes $A\rightarrow B$ dependency preserves $B\rightarrow C$ dependency also preserves $C \rightarrow D and D \rightarrow B$ i.e.$C \rightarrow B$ But there is no cyclic dependency. So, this one not preserving dependency srestha answered Jan 23, 2017 srestha comment Share Follow See 1 comment See all 1 1 comment reply sh!va commented Jan 24, 2017 reply Follow Share https://gateoverflow.in/3371/gate2008-it-61 Sir, I wonder this link says, it is dependency preserving decomposition.. Please explain which is correct!!! 0 votes 0 votes Please log in or register to add a comment.