Editing Relational algebra (section)

== Introduction ==
Relational algebra received little attention outside of pure mathematics until the publication of [[Edgar F. Codd|E.F. Codd]]'s [[relational model|relational model of data]] in 1970.<ref>{{Cite journal |last=Maddux |first=Roger D. |date=1991-09-01 |title=The origin of relation algebras in the development and axiomatization of the calculus of relations |url=https://link.springer.com/article/10.1007/BF00370681 |journal=Studia Logica |language=en |volume=50 |issue=3 |pages=421–455 |doi=10.1007/BF00370681 |issn=1572-8730}}</ref> Codd proposed such an algebra as a basis for database query languages.

Relational algebra operates on homogeneous sets of tuples <math>S = \{(s_{j1},s_{j2}, ... s_{jn}) | j \in 1 ... m \} </math> where we commonly interpret ''m'' to be the number of rows of tuples in a table and ''n'' to be the number of columns.  All entries in each column have the same [[data domain|type]].

A relation also has a unique tuple called the '''header''' which gives each column a unique name or '''attribute''' inside the relation. Attributes are used in projections and selections.