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A relation complies with first normal form when this is not the case, and no attribute ___domain has relations as elements. Codd calls a ___domain which contains relations a "[[finitary relation|nonsimple ___domain]]", or repeating group,{{r|Codd 1970 p380-381}} while a ___domain which does not contain relations is called a "simple ___domain". Normalization to 1NF is thus a process of eliminating nonsimple domains from all relations.
Codd uses the terms ''atomic'' and ''nondecomposable'' for elements of simple domains.{{r|Codd 1970 p380-381}} Thus, an atomic value is any value which is not a relation; atomic values cannot be decomposed using [[relational algebra]] operations like selection or projection. Precisely, Codd defines an atomic value as one that "cannot be decomposed into smaller pieces by the [[DBMS]] (excluding certain special functions)"<ref name="Codd 1990">Codd, E. F. ''The Relational Model for Database Management Version 2'' (Addison-Wesley, 1990)</ref>{{rp|page=6}} and states that "values in the domains on which each relation is defined are required to be atomic with respect to the DBMS,"{{r|Codd 1990}}{{Page needed|date=May 2025}}
==Examples==
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