Re: object algebra
Date: Thu, 26 Feb 2004 18:24:12 GMT
Message-ID: <gRq%b.50106$XV2.31689_at_newssvr33.news.prodigy.com>
"Neo" <neo55592_at_hotmail.com> wrote in message
news:4b45d3ad.0402251424.27581264_at_posting.google.com...
> > > Reality doesn't always provide data that fits "rectangularish"
relations.
> > > And when it doesn't, RDM needs NULLs, as Codd has correctly
recognized.
> >
> > I also find odd the idea that "reality ... provide[s] data."
>
> It was a figurative expression meaning reality can be the source for
> providing values in a relation's tuples. Reality may provide a person
> with two eyes and a person with no eyes. In RDM, the rules say define
> a relation's header at time X. RDM's rules forces us to presuppose
> that the attributes of future tuples will fit the definition at time
> X. This is rectangularish in nature. At time Y, we encounter Mary, and
> reality can't provide Mary's eyeColor so RDM create a NULL.
RDM doesn't create a null. Only an incorrect database design does. The model has nothing to do with it, unless by "model" you're referring to your specific database design. RDM as a general model is fine. Received on Thu Feb 26 2004 - 19:24:12 CET