Boyce-Codd Normal Form (BCNF)

Boyce-Codd Normal Form (BCNF) is a slightly stronger version of Third Normal Form (3NF) and is considered the gold standard for most relational database designs. A table is in BCNF if and only if for every one of its non-trivial functional dependencies X → Y, X is a superkey of the table. In simpler terms, this means that the determinant of every functional dependency must be a candidate key. While 3NF allows a non-key attribute to be determined by another non-key attribute in some rare cases (specifically in tables with multiple, overlapping candidate keys), BCNF forbids this entirely. Every table that is in BCNF is also in 3NF. However, a table in 3NF is not necessarily in BCNF. The violation of BCNF occurs in specific scenarios where a table has more than one candidate key, the candidate keys are composite, and they overlap (share at least one attribute). For example, consider a table `Student_Course_Tutor` with columns (`student_id`, `course_id`, `tutor_id`), where each student has one tutor for a specific course, and each tutor teaches only one course. The candidate keys could be (`student_id`, `course_id`) and (`student_id`, `tutor_id`). This table is in 3NF but not BCNF because `tutor_id` determines `course_id`, but `tutor_id` is not a superkey. To fix this, you would decompose it into two tables. For most practical purposes, achieving 3NF is sufficient, but understanding BCNF ensures the highest level of normalization.