Boyce Codd Normal Form (BCNF)

The Boyce Codd Normal Form is also known as 3.5NF since it is a higher version of 3NF which was developed to handle specific sorts of anomalies that 3NF did not solve. Once again, the table must fulfill the 3rd Normal Form before continuing to BCNF. Moreover, every Right-Hand Side (RHS) attribute of the functional dependencies should be dependent on the table's super key.

Now, let’s look at an example in order to better understand the principle of BCNF:

Moreover, note that one Department can be run by multiple Managers, but one Manager can only run one Department. This means that there is a dependency between the Department and the Manager attributes, i.e. the department depends on the manager’s ID (ManagerID -> Department).

You might wonder: why would this be a problem?

Well, the problem here is that the Department is a prime attribute, while the ManagerID is not a primary attribute, therefore, the table doesn’t satisfy the BCNF. In order to solve this issue and put the table in Boyce Codd Normal Form, we have to split the table into two tables, as shown below: