Functional Dependencies in Schema Design

Introduction

Functional dependencies are a crucial concept in database design that help to ensure data integrity and reduce redundancy. Understanding functional dependencies enables database designers to create normalized schemas that improve the efficiency and reliability of database operations.

Key Definitions

• Functional Dependency (FD): A relationship that exists when one attribute uniquely determines another attribute. For example, if attribute A determines attribute B, we write A → B.
• Full Functional Dependency: A functional dependency X → Y is a full functional dependency if removal of any attribute from X means the dependency does not hold anymore.
• Transitive Dependency: A functional dependency X → Z is transitive if there exists an intermediate attribute Y such that X → Y and Y → Z.

Step-by-Step Process

Identifying Functional Dependencies

1. Examine the data attributes and their relationships.
2. Determine which attributes can uniquely identify other attributes.
3. Document the functional dependencies in a tabular format.

Normalization Steps

1. Identify all functional dependencies in the schema.
2. Group attributes into relations based on these dependencies.
3. Eliminate transitive dependencies to achieve Third Normal Form (3NF).

Flowchart for Functional Dependency Analysis

graph TD;
    A[Start] --> B[Identify Attributes]
    B --> C[Determine Dependencies]
    C --> D[Document FDs]
    D --> E[Normalize Schema]
    E --> F[End]
            

Code Examples

Consider a simple relation Employee with attributes EmployeeID, Name, DepartmentID, and DepartmentName.

Employee(EmployeeID, Name, DepartmentID, DepartmentName)

Functional Dependencies:
1. EmployeeID → Name
2. DepartmentID → DepartmentName
3. EmployeeID → DepartmentID
                

From the above, we can see that DepartmentID is transitively dependent on EmployeeID, and we need to refine our schema accordingly.

Best Practices

• Always document functional dependencies when designing a schema.
• Use normalization techniques to minimize redundancy.
• Regularly review and refine schemas as new data and relationships emerge.
• Ensure that all attributes in a relation are dependent on the primary key.

FAQ