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Fourth Normal Form
A relation scheme R with set of FDs and MVDs FM is in 4NF if (and only if) for every non-trivial mvd X Y FM+ X is a superkey (for R).
A database scheme D = {R1,..., Rn} is in 4NF if (and only if) i {1,...,n}: Ri is in 4NF.
Decomposition into 4NF is done in the same way as decomposition into BCNF (but with X Y or X Y instead of just X Y in every decomposition step).
Notes: