Django Design Patterns and Best Practices - Second Edition

Third normal form (3NF)

In third normal form, the tables must satisfy the second normal form and should additionally satisfy the condition that all non-primary key columns must be directly dependent on the entire primary key and must be independent of each other.

Think about the Country column for a moment. Given the Latitude and Longitude, you can easily derive the Country column. Even though the country where a superpower was sighted is dependent on the Name-Power composite primary key, it is only indirectly dependent on them.

So, let's separate the location details into a separate countries table as follows:

Location ID	Latitude*	Longitude*	Country
1	+40.75170	-73.99420	USA
2	+35.68330	+139.73330	Japan