Re: Multiple-Attribute Keys and 1NF
Date: Tue, 28 Aug 2007 10:15:28 -0700
On Aug 28, 5:27 pm, paul c <toledobythe..._at_oohay.ac> wrote:
> JOG wrote:
> > ...
> > Brown -> live.
> > Red -> live
> > Blue -> neutral.
> > Black -> neutral.
> > Green and yellow -> earth.
> > ...
> Hey JOG, if you think that's cumbersome, try describing a typical
> motorcycle or car's wiring diagram. Unlike the your UK domestic wires
> the colour combinations are often not so nice and disjoint, eg.,
> different parallel circuits have permutations of colours, so you might
> have a Blue-White wire as well as a White-Blue wire!
> Personally, I'm not bothered at all in letting 1NF allow a key that
> names an rva, although it might be thought unwieldy by some UI
> programmers. It bugs me more that it won't work for motorcycles. For
> those, I'd need more than one relation, eg.,
> Colour Polarity
> ------ --------
> Yellow Positive
> Black Negative
> Blue Positive
> Colour Stripe Polarity
> ------ ------ --------
> Blue White Positive
> White Blue Negative
> Plus, there are so many exceptions that you have to add in manufacturer,
> year and model as attributes, eg., IIRC ground/earth for Honda's is
> usually green but not so for Suzuki/Yamaha/Kawasaki. For all I know
> Harley-Davidson's use the US domestic house wiring colours, ha ha.
> If one wants to minimize rva's, why not use two relations for the UK
> house wiring colours? (When it comes to UI programming, there will
> always be "jobs for the boys"!)
Received on Tue Aug 28 2007 - 19:15:28 CEST