Database Normalisation Questions Long
The Boyce-Codd normal form (BCNF) is a higher level of database normalization that ensures the elimination of certain types of data anomalies. It is used to address the issues that may arise when a relation (table) in a database contains functional dependencies that are not fully dependent on the primary key.
BCNF is based on the concept of functional dependencies, which are relationships between attributes in a relation. A functional dependency occurs when the value of one or more attributes determines the value of another attribute. For example, in a relation that stores employee information, the employee ID determines the employee name and department.
To be in BCNF, a relation must satisfy the following conditions:
1. Every determinant (attribute or set of attributes that determines the value of another attribute) must be a candidate key. This means that no non-key attribute should be functionally dependent on any proper subset of a candidate key.
2. There should be no non-trivial functional dependencies between candidate keys. A non-trivial functional dependency means that the determinant is not a superkey.
BCNF is used when a relation has functional dependencies that violate the second condition of BCNF. This means that there are non-trivial functional dependencies between candidate keys. By decomposing the relation into smaller relations, each satisfying BCNF, we can eliminate these anomalies.
The process of achieving BCNF involves decomposing the original relation into multiple smaller relations, each with its own primary key. This decomposition is done by identifying the functional dependencies and creating separate relations for each dependency. The resulting relations are then connected through foreign keys to maintain the relationships between the data.
BCNF helps in improving data integrity and reducing redundancy by eliminating update, insertion, and deletion anomalies. It ensures that each attribute in a relation is functionally dependent on the primary key and nothing else. However, achieving BCNF may result in a higher number of tables and more complex queries, which can impact performance and maintainability. Therefore, it is important to carefully analyze the requirements and trade-offs before applying BCNF to a database schema.