The Boyce-Codd Normal Form (BCNF) is an advanced version of the Third Normal Form (3NF) and is used to handle certain types of anomalies that 3NF cannot resolve. BCNF ensures a stricter level of normalization by addressing dependencies involving candidate keys, eliminating redundancy, and ensuring data integrity.

Note: For a table to be in BCNF, it must first be in 3NF. However, unlike 3NF, BCNF also requires that all dependencies involve only superkeys.

Requirements of BCNF

To satisfy the requirements of BCNF:

1. The table must already be in 3NF.
2. For every functional dependency X → Y, X should be a superkey. This means that X should uniquely identify every row in the table.

Example: Student_Course_Instructor Table

Let’s consider a Student_Course_Instructor table, which records students enrolled in courses and the instructors assigned to each course. In this example:

• A Course_ID can only be taught by a single instructor.
• A Student_ID can enroll in multiple courses.

Functional Dependencies

1. Student_ID, Course_ID → Instructor: Each Student_ID and Course_ID pair uniquely determines the Instructor.
2. Course_ID → Instructor: The Instructor depends on the Course_ID since each course is taught by only one instructor.

Identifying a BCNF Violation

While the table is in 3NF, it does not satisfy BCNF. This is because of the functional dependency Course_ID → Instructor:

• Course_ID is not a superkey for the table, even though Course_ID determines Instructor.
• This violates the BCNF rule since Instructor is dependent on Course_ID, which is not a superkey.

Converting to BCNF

To achieve BCNF, we need to split the table into two tables to ensure every determinant is a superkey.

Step 1: Create the Course_Instructor Table

The Course_Instructor table will contain the relationship between Course_ID and Instructor, with Course_ID as the primary key.

Step 2: Create the Student_Course Table

The Student_Course table will keep track of which courses each student is enrolled in, with the composite key (Student_ID, Course_ID).

Result After Conversion to BCNF

After splitting:

• Course_ID is a superkey in the Course_Instructor table, satisfying the BCNF requirement.
• (Student_ID, Course_ID) is the composite primary key in the Student_Course table, also satisfying BCNF.

Why BCNF is Important

BCNF is crucial for:

• Eliminating Redundancy: By ensuring all functional dependencies involve superkeys, BCNF prevents redundant data storage.
• Improving Data Integrity: The stricter rules of BCNF make data modification easier and more consistent, reducing anomalies.
• Optimizing Database Structure: BCNF provides a more streamlined database structure that reduces storage requirements and improves query performance.

In the next lesson, we’ll explore Higher Normal Forms (4NF and 5NF), which address multi-valued dependencies and join dependencies for more complex database designs.