**BCNF (Boyce Codd Normal Form) : Introduction**

**BCNF is known as “Boyce Codd Normal Form” and is a successor to “Third Normal Form”. It is used to check whether a given relation is in “BCNF” or not.****Any relation to be in BCNF must follow below mentioned two rules.****The relation/table needs to be in 3NF.****For a functional dependency P Q, “P” should be a super key.**

**BCNF deals with the cases where “Non-Prime in a functional dependency derives a prime attribute”. How? Let’s take an example to clear this doubt.**

**BCNF : Example**

**Consider a relation R(X,Y,Z) having following functional dependencies :**

**FD1 : XY Z**

**FD2 : Z Y**

**Step-1 : Check whether given relation is in 3NF or not. **

**Attribute “Z” is fully dependent upon the candidate key “XY” and there is not transitive dependency too. Also, “X & Y” are prime attributes whereas “Z & T” are non-prime attributes.**

**Step-2 : As it is confirmed that the relation is in 3NF, we can move further. Now, check for FD’s where a non-prime attribute determines a prime attribute. In this example “Z Y” is that FD.**

**FD1 : XY Z (“XY” is the candidate key, so no problem in this FD)**

**FD2 : Z Y (Here, a non-prime attribute is deriving a prime attribute)**

**Hence, we can conclude by observing “FD2” that this relation “R” is not in BCNF. Follow step-3 to convert this into BCNF.**

**Step-3 : Decompose the relation R(X,Y,Z,T) into R1(X,Y,Z) and R2(Z, Y) to convert the relation in BCNF.**

**R1 : XY Z**

**R2 : Z Y**

**“XY” and “Z” are super keys of their respective relations i.e. “R1” and “R2” as each of them can uniquely determine the attributes present in the relations.**

**Hence after decomposition, both the relations R1 and R2 are in BCNF.**