Re: Multiple-Attribute Keys and 1NF

On Aug 29, 6:10 am, "David Cressey" <cresse..._at_verizon.net> wrote:
> "JOG" <j..._at_cs.nott.ac.uk> wrote in message
>
> news:1188327226.729673.127810_at_r34g2000hsd.googlegroups.com...
>
> > Okay, sure. But then to be able to query for green and yellow
> > individually one must employ a further relation encoding two more
> > propositions that state "'Green and yellow' contains 'Green'" and that
> > "'Green and yellow' contains 'Yellow'" respectively. One then has a
> > schema with two domains - one for the composites and one for
> > individual colours (which is what I was inferring when I initially
> > said a new one was being added).
>
> It took me a while to realize that what you meant from your original
> description was that
> "a green and yellow wire means earth". I had thought you meant "a green
> wire means earth" and "a yellow wire means earth". Pardon me for being
> dense.
>
> Clearly what we have here is not a domain of colors, but a domain of color
> codes, where a color code contains one or more colors, and maybe a "thick
> or thin" qualifier on each color.
>
> It's not clear to me why you need to able to query on simple colors, unless
> you need to decompose the color coding scheme into its constituent parts for
> some reason.
>
> There are lot of code domains where each code is made up of a set of more
> primitive elements.
> Perhaps a very relevant one might be "character code". If I have the
> following primitive elements:
>
> B1, B2, B4, B8, B16, B32, B64, B128
> (which might be an odd way of labelling bits 0 through 7 of a byte), I can
> think of the character code for 'A' as being B64+B1. Now I could query on
> all the character codes without necessarily having an operator that would
> yield "all the codes that include B1".
>
> I think that the colors, as constituents of color codes, play the same role
> as bits, as constituents of character codes. Do you agree?

Yes. I mean no. No, yes. Gnngh ;)

Ok, of course I understand your point - a wire can be viewed as having a colour code, which itself has constituent parts. But its just one interpretation right. I am still seeing a difference between the propositions:
* There is a colour-code "yellow and green" that denotes "earth". * The casing of an earth wire features the colour yellow and the colour green.

Its just like the difference between the propositions: * My office is B42
* My office is on floor B, room 42.

There are instances where I may well want to encode as the second proposition forms. And /if/ that were the case (iff), well 1NF is precluding me from doing this in terms of the wire example. Received on Wed Aug 29 2007 - 12:55:26 CEST