Define Functional Dependency.

Definition of Functional Dependency

A functional dependency is a relationship between two attributes, where one attribute determines or defines the value of another. In other words, it is a logical connection between two variables that ensures data consistency across different tables or databases.

What is a Functional Dependency?

A functional dependency is a fundamental concept in database design and normalization. It states that if an attribute depends on another attribute, then the dependent attribute must be included in every row of the table where the independent attribute has a certain value.

Types of Functional Dependencies

1. Absorption: A functional dependency is said to be absorbed by another if the second attribute determines it. For example, in a database for storing information about employees, the department number determines the employee's job title.
2. Transitivity: If an attribute depends on another attribute and that attribute also depends on another attribute, then all three attributes are functionally dependent on each other. For instance, if a customer's age is determined by their date of birth, which in turn is determined by the year they were born, then all these attributes are functionally dependent.
3. Redundancy: A functional dependency can be redundant, meaning that one attribute determines another, but there is no need to store the second attribute because it can be calculated from the first. For example, in a database for storing information about products, if the product's price depends on its quantity, then the quantity does not need to be stored separately.

Example of Functional Dependency

Suppose we have two tables: Employees and Departments. Each employee belongs to one department, and each department has a certain number of employees.

In this example, the department number (Dno) determines the employee's department name (DeptName). If we change the department number, the department name will also change to ensure data consistency.

Purpose of Functional Dependency

The purpose of functional dependency is to ensure that the data in a database is consistent and up-to-date. By identifying which attributes depend on other attributes, we can create relationships between tables and avoid data inconsistencies.

Conclusion

In conclusion, functional dependency is an essential concept in database design and normalization. It helps us identify relationships between attributes and ensures data consistency across different tables or databases.

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