Re: object algebra
Date: Tue, 24 Feb 2004 21:52:29 GMT
Message-ID: <xIP_b.17536$Tr4.6294_at_newssvr31.news.prodigy.com>
"Neo" <neo55592_at_hotmail.com> wrote in message
news:4b45d3ad.0402241308.680a4901_at_posting.google.com...
> > In any event, a relation is a predicate.
>
> The above definition of a relation is significantly incomplete
> according to RDM. See Date's Chapter 4, section 3.
I wasn't being precise or complete. Predicates are the underlying motivations for all relations, however.
> Sometimes it is reality doing the hand-waving. For example a person
> may not have any eyes, but the relation's heading has eyeColor
> defined.
See my previous message.
> The core problem is not about subtyping but RDM's failure to handling
> missing data as describe by Date in Chapter 20, Missing Information.
Short version: missing data can be easily modeled as such. No need for nulls.
- erk