Fourth Normal Form


Fourth Normal Form (4NF) is a level of database normalization that involves the removal of multivalued dependencies in a table. In 4NF, a table should have no non-trivial multivalued dependencies other than functional dependencies, which ensures each attribute becomes independent and fully dependent on the primary key. This normal form reduces the redundancy and anomalies that might occur in a relational database.


The phonetic pronunciation of “Fourth Normal Form” is:/ˈfɔrθ ˈnɔrməl fɔrm/It can be pronounced as “for-th nor-muhl form”.

Key Takeaways

  1. Fourth Normal Form (4NF) focuses on the removal of multi-valued dependencies in a relation, ensuring that each attribute only depends on the primary key.
  2. In order to achieve 4NF, a relation must already be in Boyce-Codd Normal Form (BCNF). This means that all redundancy due to functional dependencies is removed, and the only remaining redundancy can be due to multi-valued dependencies.
  3. When a relation is in Fourth Normal Form, it mitigates redundancy and update anomalies caused by multi-valued dependencies, improving data integrity and consistency in the database.


The Fourth Normal Form (4NF) is a crucial concept in database normalization, as it helps maintain data consistency, integrity, and reduce redundancy within a relational database.

By ensuring that a table has no multi-valued dependencies, 4NF supports efficient querying, prevents data anomalies, and simplifies data manipulation.

In essence, it extends the principles of Third Normal Form, further enhancing the database design by eliminating complex relationships between attributes, allowing for cleaner database schema, and improving overall database performance.


Fourth Normal Form (4NF) is a critical aspect of database normalization, a technique often employed by developers to ensure the logical and efficient organization of data in a relational database. The primary purpose of 4NF is to eliminate data redundancies and anomalies resulting from multi-valued dependencies, fostering precise representation and efficient management of intricate data relationships. Achieving 4NF helps avoid insertion, deletion, and update anomalies, reducing the likelihood of inconsistencies within the database.

Besides, it improves the database’s overall efficiency, scalability, and performance, making it a vital tool in designing and maintaining complex information systems. Implementing 4NF often necessitates dividing data into smaller, more focused tables connected by a unique key. Consequently, this eliminates multi-valued dependencies and prevents the distortion or duplication of data.

By adhering to 4NF principles, developers can guarantee the integrity and consistency of their information systems, enabling smoother data retrieval and modification processes. Besides enhancing the quality of analysis and reporting, 4NF also promotes the simplification of application development tasks, simplifying data queries and changes made to the database. Overall, Fourth Normal Form plays an indispensable role in maintaining the structural efficiency, accuracy, and reliability of relational databases.

Examples of Fourth Normal Form

Fourth Normal Form (4NF) is a level of database normalization that aims to reduce data redundancy, improve data integrity, and ultimately increase database efficiency. It requires the removal of tables with multi-valued dependency issues and is based on the concept of independent data groups. Here are three real-world examples of when 4NF has been applied.

College Campus Enrollments:A college database tracks students’ course registrations and their participation in extracurricular clubs. This information is kept in a single table with columns: Student_ID, Course_ID, and Club_ID. However, Course_ID and Club_ID are independent of one another. By applying 4NF, the table is split into two separate ones – one for course registrations and another for club memberships – to eliminate the multi-valued dependency and redundancies.

Employee Skills and Training:A company’s HR database contains an Employee table with columns: Employee_ID, Skill, and Training_Course. Employees can have multiple skills and may attend multiple training courses. Since skills and training courses are independent, having them in the same table leads to multi-valued dependencies and redundancy. Applying 4NF would separate this table into two: one for employee skills and another for employee training.

Product Supplier and Customer Reviews:An e-commerce platform tracks product suppliers and customer reviews within a single table containing columns: Product_ID, Supplier_ID, Customer_ID, and Review. Both Supplier_ID and Review depend on Product_ID but are independent of each other. By applying 4NF, this table would be separated into two: one consisting of Product_ID and Supplier_ID, and the other containing Product_ID, Customer_ID, and Review. This ensures data integrity and better database efficiency.

FAQ: Fourth Normal Form

What is Fourth Normal Form?

Fourth Normal Form (4NF) is a level of database normalization used to organize the tables in a relational database and reduce data redundancy. It builds upon and extends the requirements of the Third Normal Form (3NF) by further addressing issues related to multivalued dependencies in the data schema.

Why is Fourth Normal Form important?

Fourth Normal Form is important for maintaining the consistency, integrity, and accuracy of your database. By eliminating multivalued dependencies, it ensures that the changes you make in one part of your database do not unintentionally affect other parts. This keeps your database organized, prevents redundant data storage, and reduces update anomalies.

How do you achieve Fourth Normal Form?

To achieve Fourth Normal Form, a database table must first be in Third Normal Form (3NF) which means that all non-prime attributes are fully functionally dependent on the primary key, and there is no transitive functional dependency. Then, you need to remove any multivalued dependencies in the table by decomposing it further into smaller related tables.

What are multivalued dependencies?

Multivalued dependencies occur when two or more independent attributes in a table are functionally dependent on another attribute (usually the primary key), but not on each other. In such cases, the unrelated attributes can lead to redundancy in the table as the same information is repeated for each combination of the independent attributes.

What is an example of Fourth Normal Form?

If you have a table called “Students_Courses_Hobbies” with the columns “StudentID”, “Course” and “Hobby”, you may observe that some students are enrolled in multiple courses and have multiple hobbies. The table might have multivalued dependencies because both “Course” and “Hobby” are independent and dependent on “StudentID”. To achieve Fourth Normal Form, you would split this table into two separate tables: “Students_Courses” and “Students_Hobbies”, where you would store the relationships between students and their courses, and between students and their hobbies, respectively.

Related Technology Terms

  • Dependency Preservation
  • Multi-valued Dependency
  • Database Normalization
  • Boyce-Codd Normal Form (BCNF)
  • Functional Dependency

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