Functional Dependency


Functional dependency is a concept in relational database theory that refers to the relationship between attributes in a database table. Specifically, it means that the value of one attribute (or a group of attributes) can uniquely determine the value of another attribute. This concept is used to establish data integrity and maintain efficient database design through normalization.


The phonetics of the keyword “Functional Dependency” can be represented using the International Phonetic Alphabet (IPA) as:/ˈfʌŋkʃənl dɪˈpɛndənsi/Here’s the breakdown of the phonetics:Functional:/ˈfʌŋkʃənl/Dependency:/dɪˈpɛndənsi/

Key Takeaways

  1. Functional Dependency is a relationship between two attributes, where one attribute (the determinant) uniquely determines the values of another attribute (the dependent).
  2. Functional Dependencies play a crucial role in normalization, facilitating the process of decomposing relations to improve data quality and eliminate redundancies, inconsistencies, and anomalies.
  3. Armstrong’s axioms, which are a set of inference rules, are used to derive all functional dependencies in a given dataset. They are the basis for formal reasoning regarding functional dependencies.


Functional dependency is a crucial concept in the field of database management systems and relational database theory, as it helps to establish relationships between attributes within a table and ensure data integrity and efficiency.

By defining the dependency between two attributes, where the value of one attribute (the determinant) uniquely determines the value of another attribute (the dependent), functional dependency reduces redundancy and inconsistency within a database.

This concept forms the basis for normalization, a process where database designers organize tables and their attributes, enabling the database to scale well while minimizing storage costs and improving performance.

Ultimately, functional dependency is vital to maintaining the overall accuracy, longevity, and user-friendliness of modern database systems.


Functional Dependency is a vital concept in the realm of database management and normalization, which aims to optimize the organization of data by reducing data redundancy and improving data integrity. It serves as a foundational principle to ensure that the relationships within a database are accurately represented, and the data can be efficiently queried and accessed. Primarily utilized in relational database design, functional dependency enables the identification of the correlation between attributes within a relation.

This connection is essential for providing the basis for the normalization process, which breaks down complex tables into simpler, more manageable ones. As a result, functional dependencies are used to establish rules that govern relationships between data elements and create a stable database structure. To further illustrate its significance, functional dependency is based on how an attribute’s value is determined by another attribute or a group of attributes within a relation.

For instance, if each employee in a company can be identified by a unique employee ID, their name, address, and salary are functionally dependent on their employee ID. This dependency not only ensures that data is well-organized but also enhances the performance of database operations, such as retrieval, insertion, modification, and deletion of records. In addition, functional dependencies are employed when defining various normal forms of a database schema, including First Normal Form (1NF), Second Normal Form (2NF), and Third Normal Form (3NF). Consequently, functional dependency plays a pivotal role in establishing data consistency, preventing database anomalies, and fostering an efficient and scalable database design.

Examples of Functional Dependency

Functional dependency is a constraint between two sets of attributes in a relational database. It occurs when the value of one attribute (or set of attributes) uniquely determines the value of another attribute (or set of attributes). Here are three real-world examples:

Student Enrollment System:In a university’s student enrollment system, a student’s unique identification number (StudentID) determines the student’s name, date of birth, and contact details. In this case, there is a functional dependency between the StudentID (the determinant) and the student’s personal details. This functional dependency allows the database to maintain the integrity and consistency of the data, and helps prevent the same student from being entered into the database multiple times with different names or personal details.

Product Inventory:In an online shopping platform’s product inventory database, the product code (ProductID) uniquely determines a product’s details, such as name, category, description, price, and supplier. Here, there is a functional dependency between the ProductID and product details. This functional dependency ensures that the platform’s database is consistent, providing accurate information about product availability and preventing errors like duplicate entries or sold-out products being ordered.

Employee Management System:In a company’s employee management database system, the employee number (EmployeeID) uniquely determines an employee’s name, position, department, hire date, and salary. In this context, there is a functional dependency between the EmployeeID and various employee attributes. Implementing this functional dependency is crucial for keeping the database consistent while performing operations like updating employee records, handling promotions, or managing salaries, ultimately avoiding inconsistencies and errors that could impact the efficiency and productivity of the organization.

Frequently Asked Questions about Functional Dependency

1. What is Functional Dependency?

A functional dependency is a constraint between two sets of attributes in a relation from a database. It occurs when one attribute, or a combination of attributes, is able to determine another attribute uniquely. This concept is used to establish relationships between attributes and to normalize the database design.

2. What is the role of Functional Dependency in Database Normalization?

Functional Dependencies play a crucial role in the process of database normalization. They help to identify redundant and non-atomic data, which in turn allows us to decompose the database into smaller, well-structured relations. These smaller relations eliminate redundancy and anomalies (insertion, deletion, and update anomalies), resulting in an efficient and well-designed database.

3. What is the difference between Full Functional Dependency and Partial Dependency?

Full Functional Dependency occurs when a non-prime attribute is determined solely by the entire primary key, and not by any of its subsets. Partial Dependency, on the other hand, occurs when a non-prime attribute is determined by a subset of the primary key. Full Functional Dependency is a desirable property for database normalization, while partial dependencies should be eliminated during the normalization process.

4. What is Transitive Functional Dependency?

Transitive Functional Dependency occurs when an attribute X depends on an attribute Y, and attribute Y depends on an attribute Z, making attribute X transitively dependent on attribute Z. In other words, if X -> Y and Y -> Z, then X -> Z is a transitive functional dependency. Transitive dependencies should be removed during the normalization process for a well-structured database design.

5. What is the importance of Armstrong’s Axioms in Functional Dependency?

Armstrong’s Axioms are a set of rules that are used to infer all the possible functional dependencies in a relation, given a set of initial functional dependencies. These axioms are Reflexivity, Augmentation, Transitivity, Union, Decomposition, and Pseudotransitivity. They provide a systematic approach to reasoning about functional dependencies and help in the process of database design and normalization.

Related Technology Terms

  • Normalization
  • Attribute Closure
  • Database Schema
  • Relational Database
  • Armstrong’s Axioms

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