Elementary key normal form (EKNF) is a subtle enhancement on

third normal form Third normal form (3NF) is a database schema design approach for relational databases which uses normalizing principles to reduce the duplication of data, avoid data anomalies, ensure referential integrity, and simplify data management. It was d ...

, thus EKNF tables are in 3NF by definition. This happens when there is more than one unique

compound key 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 which each attribute that m ...

and they overlap. Such cases can cause redundant information in the overlapping column(s).

History

EKNF was defined by Carlo Zaniolo in 1982.

Definition

A table is in EKNF

if and only if In logic and related fields such as mathematics and philosophy, "if and only if" (often shortened as "iff") is paraphrased by the biconditional, a logical connective between statements. The biconditional is true in two cases, where either bo ...

all its elementary functional dependencies begin at whole keys or end at elementary key attributes. For every full

non-trivial In mathematics, the adjective trivial is often used to refer to a claim or a case which can be readily obtained from context, or a particularly simple object possessing a given structure (e.g., group, topological space). The noun triviality usual ...

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 In mathematics, a Set (mathematics), set ''A'' is a subset of a set ''B'' if all Element (mathematics), elements of ''A'' are also elements of ''B''; ''B'' is then a superset of ''A''. It is possible for ''A'' and ''B'' to be equal; if they a ...

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.

Example

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

Notes

References

* * * {{Database normalization Database normalization