A '''relational database''' is a [database] constructed and used according to
the principles set out in
''A Relational Model of Data for Large Shared Data Banks'' by E.F.Codd (in
''Communications of the ACM'' Volume 13 Issue 6, June 1970).

[EMJ]: That is really the only valid '''short''' definition. There are lots of
definitions scattered around the internet, but they tend not to agree with one
another, and very very many of them are wrong to some extent if not completely
wrong.

Many things written about '''relational databases''' are really about
'''[RDBMS%|%Relational Database Management System]'''s or about 
'''[SQL%|%Structured Query Language]''' ([SQL]).

'''Relational databases''' are probably the most widely-used kind of [database].

**Comments**

'''Relational databases''' are special in that the database ''itself'' supports 
"search with complex query" (can combine conditions with boolean operations, 
even using intermediate search results for additional queries), which simplifies 
parallelization and scaling to very large datasets.

[EMJ]: The above has been here since the second edit to this page in 2008, and 
is one of those things that is more properly about [RDBMS]s

** See Also **

   [Relational Algebra]:   

   [SQL]:   

   [Comparing Tcl database abstraction layers]:   

   [TclRAL]:   

** Resources **

   [http://www.thethirdmanifesto.com/%|%The Third Manifesto] by Hugh Darwen and C. J. Date:   A proposed foundation for future database systems presented in Databases, Types, and The Relational Model: The Third Manifesto, 3rd edition, Addison-Wesley, 2006 (ISBN: 0-321-39942-0)

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