How does BCNF address the issue of functional dependencies on a part of a candidate key?

Boyce-Codd Normal Form (BCNF) is a design rule used in databases to prevent certain types of anomalies that can occur when data is inserted, updated, or deleted. BCNF addresses the issue of functional dependencies on a part of a candidate key by ensuring that for every non-trivial functional dependency X -> Y, X is a superkey.

Here are the steps to understand how BCNF addresses the issue:

1. Understanding Functional Dependencies: A functional dependency is a constraint between two sets of attributes in a database. If attribute B is functionally dependent on attribute A, then for every value of A, there is exactly one value of B.

2. Understanding Candidate Keys: A candidate key is a set of attributes that can uniquely identify a database record without any extraneous data. Each table may have one or more candidate keys.

3. Understanding BCNF: BCNF is a stricter rule than the 3rd Normal Form. A table complies with BCNF if, for every one of its dependencies X -> Y, one of the following conditions hold:

   • X is a superkey
   • Each attribute in Y-X is a prime attribute (i.e., each attribute in Y-X is part of some candidate key)

4. How BCNF Addresses the Issue: If a database design is not in BCNF, there can be functional dependencies on a part of a candidate key. This can lead to anomalies. By ensuring that for every non-trivial functional dependency X -> Y, X is a superkey, BCNF prevents these anomalies.

In other words, BCNF ensures that the database design is such that all determinants are candidate keys, eliminating the possibility of having functional dependencies on a part of a candidate key.