What is the domain-key normal form (DK/NF) and when is it used?

The domain-key normal form (DK/NF) is a higher level of database normalization that focuses on the functional dependencies between attributes in a relation. It is used to eliminate redundancy and ensure data integrity by ensuring that every attribute in a relation is functionally dependent on the entire primary key.

In DK/NF, a relation is said to be in DK/NF if and only if every non-key attribute is functionally dependent on the entire primary key. This means that each non-key attribute must be dependent on the primary key as a whole, rather than just a subset of the key.

DK/NF is typically used in situations where there are multiple candidate keys in a relation. A candidate key is a set of attributes that can uniquely identify a tuple in a relation. When there are multiple candidate keys, it is important to ensure that all non-key attributes are functionally dependent on all candidate keys to avoid redundancy and anomalies.

By enforcing DK/NF, we can eliminate the possibility of partial dependencies, where non-key attributes are dependent on only a subset of the primary key. This ensures that the relation is free from redundancy and anomalies, leading to a more efficient and reliable database design.

To achieve DK/NF, the relation must first be in at least the third normal form (3NF), which eliminates transitive dependencies. Then, we need to analyze the functional dependencies between attributes and ensure that all non-key attributes are fully dependent on the entire primary key.

In summary, the domain-key normal form (DK/NF) is a higher level of normalization that ensures all non-key attributes are functionally dependent on the entire primary key. It is used in situations where there are multiple candidate keys to eliminate redundancy and anomalies, leading to a more efficient and reliable database design.