Normalization is a process to reduce the redundancy by removing
function dependencies BCNF (Boyece code normal form) has all
functional dependencies A to B are trivial of discriminator should
be superkey. To get relation in BCNF, Splitting the relation schema
not neccessarily preserve all functional dependency, Loss less
decomposition and dependency are main points for the normalization
sometime, it is not possible to get a BCNF decomposition that is
dependency, preserving. While 4NF has very similar definition as
BCNF. A relational Schema is in 4NF, if all multivalued
dependencies A to B are trivial and determinate A is superkey of
schema. If a relational schema is in 4nf, it is already in BCNF.
and 4NF decomposition preserve the all functional dependency. so
4NF is preferable than to have BCNF.