Re: Multiple-Attribute Keys and 1NF

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.,

Solids:
Colour Polarity
------ --------
Yellow Positive
Black Negative
Blue Positive

Stripes:
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"!)

cheers,
p Received on Tue Aug 28 2007 - 18:27:46 CEST