# Re: c.d.theory glossary - RELATION

From: x <x-false_at_yahoo.com>
Date: Mon, 26 Apr 2004 17:27:27 +0300
Message-ID: <408d1ba2\$1_at_post.usenet.com>

"Dawn M. Wolthuis" <dwolt_at_tincat-group.com> wrote in message news:c6j2ge\$ket\$1_at_news.netins.net...
> Relation:
>
> A relation is a subset of the set of ORDERED tuples (A1, A2, ... Am)
formed
> by the Cartesian cross-product of sets S1 x ... x Sm where each An is an
> element of Sn.

Codd made a distinction between a RELATION and a RELATIONSHIP. In Math a RELATION is what you described. In relational model, many would work with a RELATIONSHIP instead. A RELATIONSHIP is similar to a RELATION
A RELATIONSHIP is a subset of the set of UNORDERED tuples {"S1":A1,"S2":A2,...,"Sm":Am}
where each An is an element of Sn and "Sn" is the name of the set Sn.

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Received on Mon Apr 26 2004 - 16:27:27 CEST

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