1 / 4

# Rules for Reasoning about MVDs - PowerPoint PPT Presentation

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=V W and XY=W.

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

• 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=VW and XY=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=VW and XY=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)

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