Re: Multiple-Attribute Keys and 1NF


"JOG" <jog@xxxxxxxxxxxxx> wrote in message
news:1188327226.729673.127810@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

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?



.

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