Functional dependency

Definition

Functional dependency is a relationship that exists between two attributes, typically within a database, where one attribute uniquely determines another. This concept is fundamental in ensuring data integrity and is used to organize data efficiently. When one attribute's value can uniquely identify the value of another attribute, it signifies a functional dependency, which plays a crucial role in the normalization process of relational databases.

5 Must Know Facts For Your Next Test

1. In a functional dependency denoted as A -> B, if A is known, then B can be determined with certainty.
2. Functional dependencies help identify potential keys for tables, as they reveal relationships between attributes.
3. Understanding functional dependencies is essential for database design, particularly when creating normalized forms to minimize redundancy.
4. Not all attributes in a table are functionally dependent; some may depend on combinations of multiple attributes.
5. In higher normal forms, such as 3NF (Third Normal Form), transitive dependencies must be eliminated to maintain data integrity.

Review Questions

• How does functional dependency play a role in identifying primary keys within a database?
  • Functional dependency is essential in identifying primary keys because it helps determine which attribute or set of attributes can uniquely identify records. If an attribute A functionally determines another attribute B, then A could serve as a candidate for a primary key if it uniquely identifies each instance in the database. By analyzing these relationships, database designers can establish primary keys that ensure each record is distinct and retrievable.
• Discuss the impact of functional dependencies on the normalization process in database design.
  • Functional dependencies significantly influence the normalization process by guiding how tables are structured and how data relationships are defined. During normalization, dependencies help identify redundancies and ensure that data is organized into appropriate tables. By understanding which attributes depend on others, designers can create normalized forms that reduce duplication and improve data integrity while maintaining essential relationships.
• Evaluate the implications of violating functional dependencies in relational databases and how it affects data integrity.
  • Violating functional dependencies can lead to serious issues in relational databases, including data anomalies, inconsistencies, and redundancy. For instance, if an attribute that should depend on another does not reflect that relationship correctly, it can cause discrepancies during data retrieval and updates. This violation undermines the reliability of the database and can result in incorrect information being presented or maintained, which ultimately impacts decision-making and overall system performance.

Related terms

Primary Key: A primary key is a unique identifier for a record in a database table, ensuring that no two records have the same key value.

Normalization: Normalization is the process of organizing data in a database to reduce redundancy and improve data integrity through the use of functional dependencies.

Composite Key: A composite key is a combination of two or more attributes that together uniquely identify a record in a database table.