Re: What predicates the following relation represents

"Eric Kaun" <ekaun_at_yahoo.com> wrote in message news:ToAac.46100$jm6.6203_at_newssvr16.news.prodigy.com...
> "Mikito Harakiri" <mikharakiri_at_iahu.com> wrote in message
> news:mrmac.22$mR.124_at_news.oracle.com...
> > SALES
> > =====
> > PART SOLD
> > ---- ---
> > nuts 10
> > nuts 15
> >
> > Is SALES a legal relation? Is database really a repository of facts?
>
> Yes, a database is a repository of facts.
>
> It's a legal relation, though the external predicate to which it
corresponds
> may be nonsense. You can always define a candidate key over all the
> attributes - that doesn't mean it makes sense to do so.

Just a key. I never understood the difference between "primary" and "unique", let alone "candidate". I guess they are mathematically indistinguishable, that is why there is no decent definitions for those adjectives.

Key is fine, but what about the fact

<PART=Nuts, SOLD=0>

Is it the same as the absence of the tuple?

My humble interpretation is that the SALES table with attributes PART and SOLD is still physical model. This relation on logical level is

select PART, sum(SOLD) from SALES
group by PART Received on Wed Mar 31 2004 - 19:16:20 CEST