Editing Relational model (section)

=== Basic concepts ===
[[File:Relational database terms.svg|thumb|A relation with 5 attributes (its degree) and 4 tuples (its cardinality) can be visualized as a table with 5 columns and 4 rows. However, unlike rows and columns in a table, a relation's attributes and tuples are unordered.]]

A ''relation'' consists of a ''heading'' and a ''body''. The heading defines a [[Set (mathematics)|set]] of ''attributes'', each with a ''name'' and ''data type'' (sometimes called a ''domain''). The number of attributes in this set is the relation's ''degree'' or ''[[arity]]''. The body is a set of ''tuples''. A tuple is a collection of ''n'' ''values'', where ''n'' is the relation's degree, and each value in the tuple corresponds to a unique attribute.<ref>{{Cite web |date=2023-02-12 |title=Tuple in DBMS |url=https://www.geeksforgeeks.org/tuple-in-dbms/ |access-date=2024-08-03 |website=GeeksforGeeks |language=en-US}}</ref>  The number of tuples in this set is the relation's ''[[cardinality]]''.<ref name="professionals"/>{{rp|17–22}}

Relations are represented by ''relational [[Variable (computer science)|variables]]'' or ''relvars'', which can be reassigned.<ref name="professionals"/>{{rp|22–24}} A ''[[database]]'' is a collection of relvars.<ref name="professionals"/>{{rp|112–113}}

In this model, databases follow the ''Information Principle'': At any given time, all [[Information theory|information]] in the database is represented solely by values within tuples, corresponding to attributes, in relations identified by relvars.<ref name="professionals"/>{{rp|111}}