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

"Laconic2" <laconic2_at_comcast.net> wrote in message news:tOKdnUpZC8NPtvXcRVn-sg_at_comcast.com...
>
> "Marshall Spight" <mspight_at_dnai.com> wrote in message
> news:bVT9d.361333$Fg5.257522_at_attbi_s53...
>
> > NULLs certainly suck in a lot of ways. In the context of the
> > semi-mainstream definition of 1NF (what Alfredo would call
> > the broken definition) NULLs are hard to get away from, because
> > you need some operation like LEFT OUTER JOIN. If you
> > have Relation Valued Attributes (RVAs) and some GROUP BY
> > operator, though, you don't need NULLs even for OUTER
> > JOINs.
>
> 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?

> 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.

Marshall Received on Sun Oct 10 2004 - 02:58:50 CEST