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

"Marshall Spight" <mspight_at_dnai.com> wrote in message news:eP%9d.219935$D%.37995_at_attbi_s51...  > However, note that the result of an outer join is not necessarily a
> > relation, even if both of the operands are relations.
>
> You lost me. Do you mean something besides the part where
> there are no rows on the right corresponding to rows on the
> left, or do you mean something else?

No. I meant that an outer join can introduce NULLS, and NULLS don't belong in relations.

I hope I'm not being too dogmatic about this.
>
>
> > One of Codd's 12 rules was that a relational DBMS should have a
systematic
> > treatment of NULLS.
> >
> > That, by itself, seems to me to be an admission that the relational
data
> > model is not as abstract as the relational calculus is.
> > Not that I object, mind you.
>
> Hrmn, uh, dunno. I guess I'm not sure I believe in the "relational data
model"
> as a fixed entity, although that notion is certainly popular is some
> quarters. I myself am working on "a" relational model that doesn't have
> NULLs of any kind, although it does have a "systematic treatment of"
> optional data.
>
Sure. Nothing is unchanging in this world. Date has argued for relaxing the atomicity requirement in 1NF. And a lot of people treat that as "the current RDM", and any older version of the RDM as "archaic". Like I said, you don't need NULLS, even in the RDM. Just don't ever denormalize. Received on Sun Oct 10 2004 - 05:24:34 CEST