Re: 4 the FAQ: Are Commercial DBMS Truly Relational?
Date: Sun, 10 Oct 2004 00:58:50 GMT
Message-ID: <eP%9d.219935$D%.37995_at_attbi_s51>
"Laconic2" <laconic2_at_comcast.net> wrote in message news:tOKdnUpZC8NPtvXcRVn-sg_at_comcast.com...
>
> "Marshall Spight" <mspight_at_dnai.com> wrote in message
> news:bVT9d.361333$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.
> 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