Fourth Normal Form
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