Re: A pk is *both* a physical and a logical object.

From: Cimode <>
Date: Thu, 12 Jul 2007 05:23:00 -0700
Message-ID: <>

On Jul 12, 12:56 pm, Jan Hidders <> wrote:
> On 11 jul, 22:25, Cimode <> wrote:
> > Furthermore...
> > <<Technically a PK is *only* a physical implementation device, not a
> > logical concept at all.>>
> `When I use a word,' Humpty Dumpty said, in rather a scornful tone,
> `it means just what I choose it to mean -- neither more nor less.'
> `The question is,' said Alice, `whether you can make words mean so
> many different things.'
> `The question is,' said Humpty Dumpty, `which is to be master --
> that's all.'
> ;-)
> To answer the question, I think that is quite simple. As defined in
> the relational model it is a logical concept. As far as I know the SQL
> standard does not state that a PK implies an index (but I could be
> wrong) and then it is also there a logical concept. If it does imply
> an index then it is mixed concept because it has both logical and
> physical consequences.

One does not define a concept such as *primary key* according to its physical consequences or characteristics especially when such term is unambiguously defined in the relational model. Adding ambiguous new definitions (I am refering to SQL ANSI committee) creates nothing but unecessary complexity and confuses the hell out of practitionners.

If a car is *blue* or *runs with gas* that does not mean that *blue* or *runs with gas* defines *car*.

Considering that a primary is anything but a logical concept is nonsense. Considering on the other hand that it has physical consequences makes sense. Considering that the fact of having physical consequences *de facto* defines it a physical concept is pure utter nonsense. As I said a sign of our time... Received on Thu Jul 12 2007 - 14:23:00 CEST

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