Re: Proposal: 6NF

From: David Cressey <>
Date: Wed, 18 Oct 2006 10:29:35 GMT
Message-ID: <jmnZg.3407$5h6.1779_at_trndny04>

"Jan Hidders" <> wrote in message

> David Cressey wrote:
> >
> > Agree with dawn. When I first learned set theory, they used the words
> > "group" and "field" to describe
> > a set with one or two operators defined on it. The word "set" does not,
> > AFAIK, imply any operations.
> But it doesn't exclude their existence either. You can construct a set
> that models the Reals and then after that construction define the
> operations that model the usual operations over the Reals. As long as
> their combination satisfies the laws that are given by the standard
> abstract definition of the Reals I claim that it is fair to say that
> you have corectly modeled the Reals. Val seems to disagree.
> This is very relevant in the context of database theory because this is
> what one would do when presenting a formal model that describes the
> context of a database model: you define several sets that are your
> domains (Strings, Booleans, Integers, Rationals, Floats) and in
> addition you define operations over them (+, *, length, ...). Note
> that these function are often cross-domain (e.g. length: String ->
> Integer) and cannot be really said to belong to one domain or another.
> Does that make sense to you?

Yes, except for one thing. I'm having trouble reconciling the word "domain" as you used it above, with the usage I'm accustomed to, as in "CREATE DOMAIN" from SQL.

> -- Jan Hidders
Received on Wed Oct 18 2006 - 12:29:35 CEST

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