Difference Between 3NF and BCNF

Comparison between 3NF and BCNF

3NF and BCNF these are parts of the Database Management System (DBMS).The Key Difference between 3NF and BCNF is that BCNF does not allow transitive dependencies. This means that in BCNF, every attribute in a table must be dependent on the primary key, or on a set of attributes that uniquely identifies a row in the table.

3NF and BCNF
3NF and BCNF

Comparison Chart

  • Here is a table that summarizes the key differences between 3NF And BCNF:
3NF stands for 3rd Normal Form BCNF stands for Boyce–Codd Normal Form
3NF is less strong than the BCNF. BCNF is more strong than the 3NF.
3NF has high redundancy. BCNF low redundancy in comparison to 3NF
It is comparatively easier to achieve. It is difficult to achieve.
It can be used to achieve lossless decomposition. It is difficult to achieve lossless decomposition using BCNF.

What is 3NF?

Definition: 3NF is a normal form in database normalization that aims to eliminate transitive dependencies and reduce data redundancy. It builds upon the concepts of 1NF (First Normal Form) and 2NF (Second Normal Form).

Functional dependencies: In 3NF, every non-key attribute of a relation must be functionally dependent on the whole primary key and not on any non-prime attributes.

Example: Consider a relation called “Students” with attributes such as StudentID (primary key), StudentName, CourseCode, and CourseName. In 3NF, the non-key attributes like StudentName and CourseName should be functionally dependent on the StudentID and CourseCode, respectively, rather than being dependent on other non-prime attributes.

What is BCNF?

Definition: BCNF is a more stringent normal form than 3NF, aiming to eliminate non-trivial dependencies among attributes. It was introduced by Raymond F. Boyce and Edgar F. Codd.

Functional dependencies: In BCNF, for every non-trivial functional dependency X -> Y, X must be a superkey.

Example: Consider a relation called “Employees” with attributes such as EmployeeID (primary key), EmployeeName, Department, and Supervisor. In BCNF, the functional dependencies like EmployeeID -> EmployeeName and Department -> Supervisor should hold, ensuring that the dependencies are trivial or the determinant (X) is a superkey.


In summary, both 3NF and BCNF are essential normal forms that contribute to effective database design. While 3NF reduces redundancy and eliminates transitive dependencies, BCNF takes it a step further by eliminating non-trivial dependencies. The choice between 3NF and BCNF depends on the specific needs of the database and the trade-offs between normalization and performance. Understanding these differences empowers database designers to make informed decisions regarding the appropriate level of normalization.


Q1. Is 3NF better than BCNF?

No, 3NF and BCNF serve different purposes in database normalization. 3NF focuses on eliminating transitive dependencies, while BCNF aims to eliminate non-trivial dependencies. The choice depends on the specific requirements of the database.

Q2. Can a relation be in both 3NF and BCNF?

Yes, it is possible for a relation to be in both 3NF and BCNF if all non-trivial dependencies have been eliminated, and no transitive dependencies exist.

Q3. Is BCNF always better than 3NF?

Not necessarily. BCNF offers a higher degree of normalization by eliminating non-trivial dependencies, but it might introduce more complexity in terms of join operations. The choice depends on the specific needs of the database.

Q4. Are there any disadvantages of using 3NF and BCNF?

One potential disadvantage is the potential impact on query performance due to more complex join operations required in BCNF. Additionally, achieving BCNF might require more careful consideration during database updates.

Q5. How can I convert a relation from 3NF to BCNF?

To convert a relation from 3NF to BCNF, you need to identify non-trivial dependencies and ensure that the determinant (X) is a superkey. Decompose the relation if necessary to satisfy BCNF’s requirements while preserving functional dependencies.

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