# What is 1 NF (Normal Form) 2NF,3NF 4NF 5NF & BCNF ?

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1 NF (Normal Form)
The domain of attribute must include only atomic (simple, indivisible) values.

2NF
A relation schema R is in 2NF if it is in 1NF and every non-prime attribute A in R is fully functionally dependent on primary key.

3NF
A relation schema R is in 3NF if it is in 2NF and for every FD X —>A either of the following is true
X is a Super-key of R.
A is a prime attribute of R.
In other words, if every non prime attribute is non-transitively dependent on primary key.

4NF
A relation schema R is said to be in 4NF if for every Multivalued dependency X—>Y that holds over R, one of following is true
X is subset or equal to (or) XY = R.
X is a super key.

5NF
A Relation schema R is said to be 5NF if for every join dependency {R1, R2, …, Rn} that holds R, one the following is true
Ri = R for some i.
The join dependency is implied by the set of FD, over R in which the left side is key of R.

BCNF (Boyce-Codd Normal Form)?
A relation schema R is in BCNF if it is in 3NF and satisfies an additional constraint that for every FD X—>A, X must be a candidate key.