# Re: terminology

Date: 21 Jun 2006 23:18:42 -0700

Message-ID: <1150957122.419520.276170_at_b68g2000cwa.googlegroups.com>

U-gene wrote:

*> 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.
*

In essence, what you are just trying to establish for RDM what has
already established in math for centuries: an *indissoluble* (to use
your term) relationship between variable and value. No need to spend
hours or ellaborate on that. I prefer the mathematical inspired concept
of value holder for variable. In RDM, an attribute is nothing but an
elementary relvar, result of an intersection between the relvar defined
domain and N single value domains.
Received on Thu Jun 22 2006 - 08:18:42 CEST