Re: Nested Relations / RVAs / NFNF

From: Tony Douglas <tonyisyourpal_at_netscape.net>
Date: 28 Oct 2004 14:37:08 -0700
Message-ID: <bcb8c360.0410281337.6c0b877a_at_posting.google.com>


"Marshall Spight" <mspight_at_dnai.com> wrote in message news:<17Rfd.316248$MQ5.24677_at_attbi_s52>...
> "Kenneth Downs" <firstinit.lastname_at_lastnameplusfam.net> wrote in message news:lkkolc.9oe.ln_at_mercury.downsfam.net...
> > erk wrote:

> I note that in the type theory world, attention is paid to the appropriateness
> of associated operations. For example, one might choose to have separate
> *types* for metric units and for English units, and allow the type system
> to either prevent invalid crossovers or convert for you. Also, you can do
> things like have a separate numeric type for speed, distance, and time,
> or even things like length, area, and volume. The type of the multipy
> operation for (length, length) is area; for (length, area) is volume, etc.
>

Absolutely. This is why a type isn't just a set of values, or expressions to describe the acceptable values, it's the operators on them as well. I did a presentation with Roy Hann of Rational Commerce at the UK Ingres Users Association in June 2003 about types and databases which growled it's way through precisely this point. It's an easy read and the second half is more Ingres specific, but the first half is general. If you're interested you can read it at http://www.rationalcommerce.com/resources/domains.htm. Costin will probably blow a fuse, mind... ;)  

  • Tony
Received on Thu Oct 28 2004 - 23:37:08 CEST

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