Re: 4 the FAQ: Are Commercial DBMS Truly Relational?
Date: Sat, 09 Oct 2004 17:52:43 -0400
Message-ID: <bjm9kc.bb2.ln_at_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.
>
>
-- Kenneth Downs Use first initial plus last name at last name plus literal "fam.net" to email meReceived on Sat Oct 09 2004 - 23:52:43 CEST