Re: MV Keys

Marshall Spight wrote:
> Jon Heggland wrote:
> > marshall.spight_at_gmail.com says...
>
> [... lots of disagreement ...]
>
> I was thinking about this thread, and how we seem to be talking
> past each other, and an idea occurred to me. I notice that much
> of what you're talking about is syntactic issues, while I'm trying
> to focus on the semantic. What if we're both right?
>
> What if, in fact, the element-of-a-set is a necessary *syntactic*
> construct, but not a necessary *semantic* one?

Yes, I think that is the difference, however, I suspect Jon might disagree. You might have noticed that Jan H. challenged me when I called a tuple in the GIRLS paper a relation, so I thought about it at that time and figured that from his perspective this was a semantic issue. Are you both a person and a set of one person? I would think so, but one is a person and the other is a set. Is the lack of something an empty set? Sure, but then it is something (a set) and not just the lack of something.

> I notice you've brought up the issue of how one writes a relation
> literal a few times. Certainly, one needs a *syntactic* way to
> distinguish when one is entering values for one "row" and when
> one moves on to the next row.
>
> But at the semantic level, perhaps there is no need for a separate
> type, a separate abstraction, to model that element. The RA
> has no tuple-level operations, after all.
>
>
> > > > Yet (1,b) is obviously not a relation, and equally obviously not a tuple
> > > > by your definition! It is not the subset of anything, because it is not
> > > > a set. Do you still not see the problem?
> > >
> > > Yes, I still don't see the problem.
> >
> > The problem is that you contradict yourself. You say (1,b) is a tuple,
> > and you say that a tuple is a set. (1,b) is not a set.
>
> Syntactically, that is true. Semanticly, it may not be true.

Maybe the way to say it is that anything that can be modeled as a tuple can be modeled as a set with one tuple element. So you are right that you don't need a tuple type separate from a relation type IMO. If you have relation operators, you can take any tuple and treat it as a set of one tuple. --dawn

<snip lots of good stuff for brevity> Received on Thu Mar 09 2006 - 22:34:58 CET