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Rules for Reasoning about MVDsPowerPoint Presentation

Rules for Reasoning about MVDs

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Rules for Reasoning about MVDs

- Use to identify the MVDs (e.g., from FD to MVD) which are necessary for the decomposition of a relation into 4NF

V W is X Y with X=VW and XY=W

- V W implies that every instance of R can be losslessly decomposed into two relations R1=(V,F1) and R2=(W,F2)
- X Y implies that for every value of X are independent of the value of Y

V W is X Y with X=VW and XY=W

- If X Y then X Z for Z X Y (trivial)
- If X Y and Y Z then X Z (transitivity of MVDs)
- If X Y then X Z for Z = R – (X Y) (complementation)
- If X Y then X Y (FD implication)

Algorithm for 4NF decomposition

Similar to BCNF decomposition:

Given R = (R, D) where D contains FDs and MVDs

- Take X Y violates the 4NF condition
- Decompose R into R1=(X,D1) and R2=(X(R-Y),D2) where the FDs in D1 and D2 are computed in the same way as in the BCNF decomposition, see note for the computation of the MVDs

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