## A relation R is in 4NF if for every nontrivial X??Y, X is a superkey of R.

## Decomposition into 4NF: If there is a non-trivial X??Y, form one relation with only X and Y, and another with R-Y.

- In other words, allow only one MVD per relation

## This will be lossless, but not necessarily FD-preserving.

- Achieving 4NF is a trade-off

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