Functional dependency
(also FD, attribute dependency)
Functional dependency definition
A functional dependency is a constraint between two sets of attributes in a relationship from a database. It occurs when one set of attributes (called the determinant) uniquely determines another set of attributes (called the dependent). The functional dependency is used to establish relationships and design efficient database schemas while avoiding redundancy and ensuring data consistency.
Functional dependency examples
A functional dependency is a constraint between two sets of attributes in a relationship from a database. It occurs when one set of attributes (called the determinant) uniquely determines another set of attributes (called the dependent). The functional dependency is used to establish relationships and design efficient database schemas while avoiding redundancy and ensuring data consistency.
Functional dependency vs. other constraints
- Functional dependency vs. referential integrity: Functional dependencies focus on attributes within a relationship, whereas referential integrity enforces relationships between different relations in a database.
- Functional dependency vs. primary key: A primary key is a minimal set of attributes for uniquely identifying a record or tuple in a relationship. It forms a functional dependency, where the primary key is the determinant, and all other attributes in the relation are dependents.
Pros and cons of functional dependencies
Pros:
- Enables normalization, which reduces data redundancy and improves data consistency.
- Helps maintain data integrity by ensuring that attribute values are uniquely determined.
Cons:
- Can increase the complexity of a database schema.
- May require additional processing overhead when updating, inserting, or deleting tuples.
Tips for working with functional dependencies
- Identify functional dependencies early in the database design process to reduce redundancy and improve data consistency.
- Use functional dependencies to sever relationships and normalize the database schema.
- Consider using functional dependency analysis tools to identify potential issues with your database design.