Elementary key normal form (EKNF) 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 {{Unreferenced, date=October 2020
In database design, a composite key is a candidate key that consists of two or more attributes (table columns) that together uniquely identify an entity occurrence (table row). A compound key is a composite key for ...
and they overlap. Such cases can cause redundant information in the overlapping column(s).
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 (a part of) an elementary key.
In this definition, an ''elementary functional dependency'' is a full functional dependency (a non-trivial functional dependency X → A such that there is no functional dependency X' → A that also holds with X' being a strict subset of X), 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.
Notes
References
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{{Database normalization
Database normalization