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Re: terminology

From: U-gene <grigoriev-e_at_yandex.ru>
Date: 21 Jun 2006 14:11:06 -0700
Message-ID: <1150924266.649153.189330@r2g2000cwb.googlegroups.com>

Just a remark

Marshall wrote:

> Most basically, a relation is a subset of a product of sets.
> In the c.d.t. context, we mean a little more than that, because
> of keys and possibly constraints, and because each of the sets
> has an associated name, but that's the basic idea. A particular
> relation is a value.

I've got a old book of David Maier "The theory of Relational Dataase" (IMHO it's only really theory book on subj). There is very interesting definition (which can be called "orthogonal" to usual one) of what relation is in this book. I'll try to translate it back form Russian to English :)

"...Relation r, which has schema R{A1, A2 ... An}, is a finitesimal set of the mappings {t1, t2 ... tn} from R to _D_, where _D_ is union of domains D1, D2.... Dn , and each mapping t(Ai) belongs to Di. ..."

I don't know if I could translate it correctly. It is interesting becouse it define indissoluble relationship between schema and body of relation. There is NO something special in schema or in body - they are just set(s) of values becouse each Ai is name(i.e. value) and each t(Ai) is (scalar) value. According to this(and all the more ) - relation is value. Received on Wed Jun 21 2006 - 16:11:06 CDT

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