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Normal Forms

Boyce-Codd Normal Form (BCNF)

Boyce-Codd Normal Form(BCNF) is an advanced version of 3NF as it contains additional constraints compared to 3NF.

  • For a relational table to be in Boyce-Codd normal form, it must satisfy the following rules:

    1. The table must be in the third normal form.
    2. For every non-trivial functional dependency X -> Y, X is the superkey of the table. That means X cannot be a non-prime attribute if Y is a prime attribute.

  • A superkey is a set of one or more attributes that can uniquely identify a row in a database table.

Let us take an example of the following EmployeeProjectLead table to understand how to normalize the table to the BCNF:

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Explanation

The above table satisfies all the normal forms till 3NF, but it violates the rules of BCNF because the candidate key of the above table is {Employee Code, Project ID}. For the non-trivial functional dependency, Project Leader -> Project ID, Project ID is a prime attribute but Project Leader is a non-prime attribute. This is not allowed in BCNF.

To convert the given table into BCNF, we decompose it into two tables:

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Thus, we’ve converted the EmployeeProjectLead table into BCNF by decomposing it into EmployeeProject and ProjectLead tables.