2021/8/8 Second normal form – Wikipedia
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Second normal form
Second normal form (2NF) is a normal form used in database normalization. 2NF was originally
defined by E. F. Codd in 1971.[1]
A relation is in the second normal form if it fulfills the following two requirements:
1. It is in first normal form.
2. It does not have any non-prime attribute that is functionally dependent on any proper subset of
any candidate key of the relation. A non-prime attribute of a relation is an attribute that is not
a part of any candidate key of the relation.
Put simply, a relation is in 2NF if it is in 1NF and every non-prime attribute of the relation is dependent
on the whole of every candidate key. Note that it does not put any restriction on the non-prime to non-
prime attribute dependency. That is addressed in third normal form.
2NF and candidate keys
See also
References
Further reading
External links
A functional dependency on part of any candidate key is a violation of 2NF. In addition to the primary
key, the relation may contain other candidate keys; it is necessary to establish that no non-prime
attributes have part-key dependencies on any of these candidate keys.
The following relation does not satisfy 2NF because:
{Manufacturer country} is functionally dependent on {Manufacturer}.
{Manufacturer country} is not part of a candidate key, so it is a non-prime attribute.
{Manufacturer} is a proper subset of {Manufacturer, Model} candidate key.
Since {Manufacturer country} is a non-prime attribute functionally dependent on a part of a candidate
key, the relation is in violation of 2NF.
Contents
2NF and candidate keys
https://en.wikipedia.org/wiki/Database_normalization#Normal_forms
https://en.wikipedia.org/wiki/Database_normalization
https://en.wikipedia.org/wiki/E._F._Codd
https://en.wikipedia.org/wiki/First_normal_form
https://en.wikipedia.org/wiki/Non-prime_attribute
https://en.wikipedia.org/wiki/Functional_dependency
https://en.wikipedia.org/wiki/Proper_subset
https://en.wikipedia.org/wiki/Candidate_key
https://en.wikipedia.org/wiki/Third_normal_form
https://en.wikipedia.org/wiki/Functional_dependency
https://en.wikipedia.org/wiki/Primary_key
2021/8/8 Second normal form – Wikipedia
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Electric toothbrush models
Manufacturer Model Manufacturer country
Forte X-Prime Italy
Forte Ultraclean Italy
Dent-o-Fresh EZbrush USA
Brushmaster SuperBrush USA
Kobayashi ST-60 Japan
Hoch Toothmaster Germany
Hoch X-Prime Germany
The relation is not in 2NF. {Manufacturer, Model} is a candidate key, and Manufacturer country is
dependent on a proper subset of it: Manufacturer. To make the design conform to 2NF, it is necessary to
have two relations:
Electric toothbrush manufacturers
Manufacturer Manufacturer country
Forte Italy
Dent-o-Fresh USA
Brushmaster USA
Kobayashi Japan
Hoch Germany
Electric toothbrush models
Manufacturer Model
Forte X-Prime
Forte Ultraclean
Dent-o-Fresh EZbrush
Brushmaster SuperBrush
Kobayashi ST-60
Hoch Toothmaster
Hoch X-Prime
Attribute-value system
See also
https://en.wikipedia.org/wiki/Attribute-value_system
2021/8/8 Second normal form – Wikipedia
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1. Codd, E. F. “Further Normalization of the Data Base Relational Model”. (Presented at Courant
Computer Science Symposia Series 6, “Data Base Systems”, New York City, May 24–25, 1971.)
IBM Research Report RJ909 (August 31, 1971). Republished in Randall J. Rustin (ed.), Data Base
Systems: Courant Computer Science Symposia Series 6. Prentice-Hall, 1972.
Litt’s Tips: Normalization (http://www.troubleshooters.com/littstip/ltnorm.html)
Date, C. J.; Lorentzos, N.; Darwen, H. (2002). Temporal Data & the Relational Model (http://ww
w.elsevier.com/wps/product/cws_home/680662) (1st ed.). Morgan Kaufmann. ISBN 1-55860-
855-9.
Date, C. J. (2004). Introduction to Database Systems (https://archive.org/details/introductionto
da0000date) (8th ed.). Boston: Addison-Wesley. ISBN 978-0-321-19784-9.
Kent, W. (1983). “A Simple Guide to Five Normal Forms in Relational Database Theory” (http://
www.bkent.net/Doc/simple5.htm). Communications of the ACM. 26: 120–125.
Database Normalization Basics (https://www.thoughtco.com/database-normalization-basics-1
019735) by Mike Chapple (About.com)
An Introduction to Database Normalization (http://mikehillyer.com/articles/an-introduction-to-
database-normalization/) by Mike Hillyer.
A tutorial on the first 3 normal forms (http://phlonx.com/resources/nf3/) by Fred Coulson
Description of the database normalization basics (http://support.microsoft.com/kb/283878) by
Microsoft
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References
Further reading
External links
http://www.troubleshooters.com/littstip/ltnorm.html
https://en.wikipedia.org/wiki/Christopher_J._Date
http://www.elsevier.com/wps/product/cws_home/680662
https://en.wikipedia.org/wiki/ISBN_(identifier)
https://en.wikipedia.org/wiki/Special:BookSources/1-55860-855-9
https://en.wikipedia.org/wiki/Christopher_J._Date
https://archive.org/details/introductiontoda0000date
https://en.wikipedia.org/wiki/ISBN_(identifier)
https://en.wikipedia.org/wiki/Special:BookSources/978-0-321-19784-9
http://www.bkent.net/Doc/simple5.htm
https://www.thoughtco.com/database-normalization-basics-1019735
http://phlonx.com/resources/nf3/
http://support.microsoft.com/kb/283878
https://en.wikipedia.org/w/index.php?title=Second_normal_form&oldid=1035922997
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