First normal form: Difference between revisions

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'''First normal form''' ('''1NF''') is a property of a [[relation (database)|relation]] in a [[relational database]]. A relation is in first normal form when no [[attribute ___domain]] has relations as elements.<ref>Codd, E.F (1972). "Further Normalization of the Data Base Relational Model". p. 27</ref> Or in [[SQL]] terminology, when no table column can have tables as values. The purpose of 1NF is to make the data model more flexible, to simplify the [[relational algebra]] and query language, and to enable further normalization levels which reduce redundancy and anomalies.<ref>Codd, E.F (1970). "A Relational Model of Data for Large Shared Data Banks". Communications of the ACM. Classics. 13 (6): 377–87. p. 380-381</ref> Standard [[SQL]] does not support creating or using table-valued columns, which means most relational databases will be in first normal form by necessity. [[Database normalization|Normalization]] to 1NF is the process of eliminating nested data records and instead representing relationships between relations through [[foreign key|foreign keys]].<ref>Codd, E.F (1970). "A Relational Model of Data for Large Shared Data Banks". Communications of the ACM. Classics. 13 (6): 377–87. p. 380-381</ref>. This in contrast to [[hierarchical database|hierarchical databases]] and [[document database|document databases]] where complex data structures are represented as nested records. Such database systems are sometimes called [[NoSQL]] systems.

==Overview==

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A ___domain which contains relations is called a [[finitary relation|nonsimple ___domain]], while a ___domain which does not contain relations is called a simple ___domain. The term ''repeating group'' is analogous to a nonsimple ___domain.<ref>Codd, E.F (1970). "A Relational Model of Data for Large Shared Data Banks". Communications of the ACM. Classics. 13 (6): 377–87. p. 380</ref> Normalization to 1NF is thus a process of eliminating nonsimple domains from all relations.

E. F. Codd uses the terms ''atomic'' and ''nondecomposable'' for elements of simple domains.<ref>Codd, E.F (1970). "A Relational Model of Data for Large Shared Data Banks". Communications of the ACM. Classics. 13 (6): 377–87. p. 380</ref>. Thus an atomic value is any value which is not a relation. Such values cannot be decomposed using just [[relational algebra]] operators like selection or projection.

== Rationale ==