Re: does a table always need a PK?

From: Heikki Tuuri <Heikki.Tuuri_at_innodb.com>
Date: Sun, 31 Aug 2003 09:16:18 GMT
Message-ID: <C1j4b.55$TR6.11@read3.inet.fi>

Paul,

"Paul G. Brown" <paul_geoffrey_brown_at_yahoo.com> kirjoitti viestissä news:57da7b56.0308310053.73e1085d_at_posting.google.com... > "Heikki Tuuri" <Heikki.Tuuri_at_innodb.com> wrote in message news:<Ovg4b.8$TR6.1_at_read3.inet.fi>...

> > Paul,
> >
> > "Paul G. Brown" <paul_geoffrey_brown_at_yahoo.com> kirjoitti viestissä
> > news:57da7b56.0308301443.21c98c43_at_posting.google.com...
> > > "Heikki Tuuri" <Heikki.Tuuri_at_innodb.com> wrote in message

...
> If the formal system provides all the necessary mechanics then it
> ought to be decidable. But in practice getting all of the mechanics
> down is very hard.

now we are coming to mathematical logic, which is my subject. Powerful formal systems are NOT decidable. That is the famous result of Kurt Gödel from about year 1930. For example, there are sentences of arithmetic which are not provable from Peano's axioms, and their negation is neither.

...
> The Relational
> Model (note the capitals) does not exist in the same sense: it is nothing
> more than a (well, several really) sets of formal definitions. Any decent
> text on the topic will describe them (or at least, one author's version > of them.)

It still is not clear to me what you mean by 'the Relational Model'. The determiner 'the' suggests there is only one 'Relational Model'. But above you say that different authors have different versions. My view is that there are several relational models, and to be precise we should refer to them by the author and the paper. That is why I am talking about Codd-1970-relational and Codd-12-relational. Codd 12 probably has no formal definition, at least no one in this discussion has been able to point out where the formal definition was published.

...
> KR

Best regards,

Heikki Tuuri
Innobase Oy Received on Sun Aug 31 2003 - 04:16:18 CDT