A table in third normal form (3NF) must be in second normal form and have no transitive dependencies.
A transitive dependency is when a non-key column’s value determines another non-key column’s value.
A table is in third normal form when non-key columns are mutually independent and dependent on only
primary key column(s).

A domain-key normal form (DKNF) is a constraint of the domain (or range of permitted values) and the keys.
The sale determines the customer. Customer depends on sale and sale is a key.
The sale determines the item. Item depends on sale and sale is a key.
The item determines the price. Price depends on item and item is a key.
One table uses sale as a key and the other table uses item as a key.