Define BCNF? How Does BCNF Differ From 3NF? Explain With An Example?

Boyce-Codd Normal Form (BCNF) is a level of database normalization that ensures that every determinant in a table is a candidate key. BCNF is a more strict form of normalization than 3NF, and is sometimes referred to as 3.5NF.

BCNF differs from 3NF in that it requires that all non-key attributes are fully dependent on the candidate keys of the table, rather than just the primary key. This means that if a table has more than one candidate key, each non-key attribute must be fully dependent on all candidate keys, rather than just one.

For example, consider a table called 'Employees' that contains the following fields: Employee_ID, Employee_Name, Employee_Department, and Department_Manager. In this table, the primary key is Employee_ID, and there is another candidate key, {Employee_Name, Employee_Department}.

While this table is normalized to 3NF, it is not in BCNF, because the Department_Manager field is only partially dependent on the primary key Employee_ID, and not on the candidate key {Employee_Name, Employee_Department}.

To normalize this table to BCNF, we need to split it into two separate tables. The first table would contain the Employee_ID, Employee_Name, and Employee_Department fields, and the second table would contain the {Employee_Name, Employee_Department} and Department_Manager fields. This would ensure that each non-key attribute is fully dependent on all candidate keys for the table.

By normalizing this table to BCNF, we can ensure that all data in the table is stored in a way that prevents update, insertion, and deletion anomalies. This can improve the efficiency and integrity of the database, and make it easier to maintain and update over time.