Re: 4 the FAQ: Are Commercial DBMS Truly Relational?

From: Kenneth Downs <firstinit.lastname_at_lastnameplusfam.net>
Date: Sat, 09 Oct 2004 17:52:43 -0400
Message-ID: <bjm9kc.bb2.ln@mercury.downsfam.net>

Marshall Spight wrote:

> "Kenneth Downs" <firstinit.lastname_at_lastnameplusfam.net> wrote in message
> news:hqd6kc.4go.ln_at_mercury.downsfam.net...

>>
>> The objection to this seems to be that the
>> RDM requires an implied unique constraint on all columns of all tables.
>> Because such a constraint is not present, they are not truly relational.
>>
>> Is that right?

>
> Yeah. I'm not sure about "implied" though.
>
> I've never seen a relation in a math textbook where the uniqueness
> constraint wasn't on all attributes, but as we all know, there's lots
> of uses for keys with fewer than the maximum number of columns,
> and even for multiple keys. These are necessarily explicit.
>
> Anyway, the definition of "relation" certainly includes a uniqueness
> requirement, no matter how you slice it.
>
>

Let's say that your DB architect has decreed that all tables must contain a last-modified timestamp, enforced by trigger during all insert/updates. This creates, by convention, a truly relational system, no? Because the timestamp is actually useful (as opposed to say some kind of IDENTITY column that is never used), it seems that one could use commercial products to produce truly relational systems?

-- 
Kenneth Downs
Use first initial plus last name at last name plus literal "fam.net" to
email me

Received on Sat Oct 09 2004 - 16:52:43 CDT