Elementary key normal form


Elementary key normal form is a subtle enhancement on third normal form, thus EKNF tables are in 3NF by definition. This happens when there is more than one unique compound key and they overlap. Such cases can cause redundant information in the overlapping column.
A table is in EKNF if and only if all its elementary functional dependencies begin at whole keys or end at elementary key attributes. For every full non-trivial functional dependency of the form X→Y, either X is a key or Y is an elementary key.
In this definition, an elementary functional dependency is a full functional dependency, and an elementary key is a key X for which there exists an attribute A such that X → A is an elementary functional dependency.
EKNF was defined by Carlo Zaniolo in 1982.

Example

For an example of a table whose highest normal form is EKNF, see Boyce–Codd normal form#Achievability of BCNF.