Oracle FAQ | Your Portal to the Oracle Knowledge Grid |
Home -> Community -> Usenet -> comp.databases.theory -> Re: completeness of the relational lattice
Just some quick comments:
On Jun 22, 11:29 am, Vadim Tropashko <vadimtro_inva..._at_yahoo.com>
wrote:
>
> Before giving the equality axiom let describe informally what the
> constant E is. We join all possible equality relations in the system,
> so that we have something like this
>
> E = `x=y` /\ `y=z` /\ ... /\ 'a=b' /\ ...
How interesting! That would have made some of the stuff I was working on a few weeks ago a lot easier. However, not having it meant I had to come up with an entirely different approach that I think has some merit, namely the "free relation variable with fixed header."
> Sure x,y,z have to belong to the same domain, while "a" and "b" may be
> from a different domain. This is again an informal definition that is
> supposed to drive the intuition.
Hmm. I don't get that. Also, is there any significance to the fact that x=y and a=b are enclosed in different kinds of quotes?
Let me just say that I think that domains are pure distraction, best ignored. The algebra needn't have domains; they complicate without adding benefit. Domains make more sense as a kind of constraint.
Marshall Received on Fri Jun 22 2007 - 19:27:28 CDT