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>
Date: Mon, 26 Apr 2004 17:27:27 +0300
Message-ID: <408d1ba2$1_at_post.usenet.com>
- Post for FREE via your newsreader at post.usenet.com ****
"Dawn M. Wolthuis" <dwolt_at_tincat-group.com> wrote in message
news:c6j2ge$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.
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
- Usenet.com - The #1 Usenet Newsgroup Service on The Planet! *** http://www.usenet.com Unlimited Download - 19 Seperate Servers - 90,000 groups - Uncensored -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=