The purpose of BCNF (Boyce-Codd Normal Form) in database normalization is to ensure that there are no partial dependencies on the primary key. It is a higher level of normalization that addresses certain anomalies.

BCNF (Boyce-Codd Normal Form) is a higher level of database normalization that helps to eliminate partial dependencies on the primary key. The purpose of BCNF is to ensure that the database is free from redundancy and anomalies, and to promote data integrity and consistency.

Partial dependency refers to a situation where an attribute depends on only a part of the primary key, rather than the entire key. This can lead to redundancy and data anomalies in the database. BCNF helps to eliminate these partial dependencies and ensures that each attribute in a table is functionally dependent on the entire primary key.

BCNF achieves this by breaking down the table into smaller tables, each having a single theme or entity. These smaller tables are then related to each other through foreign keys. This process is known as decomposition or splitting.

The process of decomposition involves the following steps:

1. Identify the functional dependencies: Analyze the functional dependencies between the attributes in the table.

2. Check for partial dependencies: Identify if there are any partial dependencies, i.e., an attribute depending on only a part of the primary key.

3. Decompose the table: If there are partial dependencies, decompose the table into smaller tables, each having a single theme or entity. The primary key of the original table becomes the primary key of the new tables, and the attributes are distributed among them based on their functional dependencies.

4. Establish relationships: Establish relationships between the smaller tables using foreign keys to maintain data integrity and consistency.

By eliminating partial dependencies, BCNF ensures that each attribute in a table is functionally dependent on the entire primary key. This improves the overall performance of the database by reducing redundancy and ensuring data consistency. It also allows for more efficient query processing, as the data is organized in a way that minimizes data duplication and improves data retrieval.

In conclusion, the purpose of BCNF is to eliminate partial dependencies on the primary key, thus improving data integrity, reducing redundancy, and enhancing database performance.