Elementary key normal form

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

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

History

EKNF was defined by Carlo Zaniolo in 1982.^[1]

Definition

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.^[1]

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.

Example

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

Notes

References

• Halpin, T. A.; Morgan, Antony J.; Morgan, Tony. Information Modeling and Relational Databases.
• Date, C. J. "Elementary key normal form (EKNF)". Database Design and Relational Theory.
• Celko, Joe. SQL for Smarties: Advanced SQL Programming (3rd ed.).