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What is Functional Dependency?
Functional dependencies are a fundamental concept in relational databases. They help ensure the accuracy and integrity of data by describing the relationships between different fields in database tables.
If we have a set of attributes A and another set of attributes B, we can say that B is functionally dependent on A (denoted as A -> B). It’s for every possible combination of values of A, there is only one corresponding combination of values for B.
Example:
- Imagine a table with attributes CourseID, CourseName, and StudentID.
- If we assume that CourseID uniquely determines CourseName.
- Because each Course ID is associated with only one Course name, we can express this as CourseID -> CourseName.
Types of Functional Dependencies
- Full Functional Dependency
- Partial Dependency
- Transitive Dependency
Full Functional Dependency
- Full functional dependency is where the dependent attribute is fully dependent on the entire set of attributes in the determinant.
- In other words, removing any attribute from the determinant would break the dependency.
Example:
- Consider a relation (table) with attributes , , and .
- We say that is fully functionally dependent on both and if, given any specific combination of values for and , there is only one corresponding value for .
- is fully functionally dependent on and .
Partial Dependency
- A type of dependency in which a non-key attribute is dependent on a part of a primary key attribute.
Example
Table Name- StudentCourse
• Attributes – StudentID, CourseID, coursename
• CourseID, –> coursename
• Specifies coursename is partially dependent on CourseID only
Transitive Dependency
A transitive dependency is a type of functional dependency in which the value in a non-key attribute is determined by the value in another non-key attribute.
Table Name- Project
• Attributes – ProjNum, ProjTitle, ProjManager, ManagerPhone
• ProjManager — > ManagerPhone
• Specifies ManagerPhone is Transitively dependent on ProjManager.
• ProjManager and ManagerPhone are non-key attributes
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