605 Boyce-Codd Normal Form (BCNF) PDF

605 Boyce-Codd Normal Form (BCNF) The Boyce-Codd Normal Form (BCNF) is an advanced version of the Third Normal Form ** ==...

605 Boyce-Codd Normal Form (BCNF) 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: * * The table must already be in 3NF. * * ** ** * 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. ** ` ` ** * * ` ` ` Student_ID ` ` Course_ID ` ` Instructor ` 101 C101 Dr. Brown 102 C101 Dr. Brown 103 C102 Dr. Smith 104 C103 Dr. Lee Functional Dependencies ** ` Student_ID, Course_ID → Instructor : ` ** Each Student_ID and Course_ID pair uniquely determines the Instructor. ** ` ` ** ** ` ` ** ** ` ` ** ** ` 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. ** ` ` ** ** **  ` Course_ID ` ` Instructor ` C101 Dr. Brown C102 Dr. Smith C103 Dr. Lee 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). ** ** ` ` ` Student_ID ` ` Course_ID ` 101 C101 102 C101 103 C102 104 C103 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. == == ==