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# 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.

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## PowerPoint Slideshow about ' Rules for Reasoning about MVDs' - gitel

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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)
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