fifth normal form

a relation schema $\text{[math]}$ is in fifth normal form (5NF) with respect to a set $\text{[math]}$ of functional, multivalued, and join dependencies if, for every nontrivial join dependency $\text{[math]}$ in $\text{[math]}$ (that is, implied by $\text{[math]}$ ), every $\text{[math]}$ is a superkey of $\text{[math]}$ .
[cite:;from @elmasri_db_2015 chapter 14.7 join dependencies and fifth normal form]

5nf generalizes 4nf to more than 2 pairs of multivalued dependencies in the key of the original relation.

dealers represent companies, and sell their products
the following schema is appropriate:

company-dealers (company, dealer)
product-dealers (product, dealer)
company-products (product, company)
sales (product, company, dealer)