Re: Question on Structuring Product Attributes

From: paul c <toledobythesea_at_oohay.ac>
Date: Sat, 16 Feb 2013 15:20:01 -0800
Message-ID: <kfp47k$n71$1_at_speranza.aioe.org>

On 14/02/2013 8:03 PM, James K. Lowden wrote:
> SQL was intended, I'm sure you agree, to be a language for deriving
> logical inferences. If SQL is "defined in the RM" as you so avidly
> believe, it should at least be logical.

James, I like your posts and agree with pretty much everything you've said lately, plus what I've noticed on your site. (I'm interested mostly only in basics so there will be details you know and care about that I don't.) I agree with your second sentence but have to quibble with the first.

 From Codd 1970: "For expository reasons, we shall frequently make use of an array representation of relations, but it must be remembered that this particular representation is not an essential part of the relational view being expounded."

Then: (such an) "array which represents an n-ary relation R has the following properties :

(1) Each row represents an n-tuple of R.
(2) The ordering of rows is immaterial.
(3) All rows are distinct.
(4) The ordering of columns is significant-it corresponds

to the ordering S1, Sz , . . . , S, of the domains on which R is defined (see, however, remarks below on domain-ordered and domain-unordered relations ).
(5) The significance of each column is partially conveyed by labeling it with the name of the corresponding domain.

It's pretty clear to me that the SQL originators missed Codd's point about this kind of array being merely for "expository reasons". So they implemented something that is more physical than the the logical kind of relations Codd had in mind. Perhaps they missed the point on purpose, I don't know about that, but the result of what might have seemed a minor detour at the time has generated nearly thirty years of confusion, SQL practioners imagining that they are using the logic Codd had in mind and imagining they are applying his model. This is exactly parallel to the old tale of the Emperor's New Clothes, walking around naked and not knowing it.

I saw your BSD youtube presentation which references your website. Another comment I have is in spite of my comments above, is that I agree that there's value in some of the existing SQL implementations. I think the main value is that they might be used as a completely physical layer by a more faithful logical implementation of Codd's idea. This might need to excise some of their silly gewgaws.

Keep up the good work. Received on Sun Feb 17 2013 - 00:20:01 CET