4NF Decomposition is the problem of decomposing a relation schema into fourth normal form (4NF). A relation schema $R^*$ is in fourth normal form (4NF) if, whenever a nontrivial multivalued dependency $X \rightarrow Y$ holds for $R^*$, then so does the functiunal dependency $X \rightarrow A$ for every column name $A$ of $R^*$. Intuitively all dependencies are the result of keys. In particular a 4NF relation schema can have no nontrivial multivalued dependencies that are not functional dependencies.