Re: Relation Schemata vs. Relation Variables

Jan Hidders wrote:
> vc wrote:
> > Jan Hidders wrote:
> > [...]
> > >. Note btw. that they are a strict
> > > subclass of the restrictions that might be expressed by some kind of
> > > temporal logic.
> >
> > What temporal logic do you have in mind ?
>
> First order logic extended with the 'since', 'until', 'next' and
> 'previous' operators.
>
> > It's known that first-order
> > temporal logic is strictly less expressive than FOL for a relational
> > database augmented in a natural way with a timestamp column, or in
> > other words FOTL is less expressive than two sorted FOL with the time
> > domain as an additional sort ( the propositional fragments of both are
> > equivalent).
>
> Indeed, even if you extend it with temporal operators for all regular
> expressions, but that is not what I was comparing it to.

So, if we are in agreement as to the FOTL expressive power, what exactly did you mean when you said that "they" (presumably constraints expressed as FOL predicates) are a " subclass of the restrictions that might be expressed by some kind of temporal logic" ? It's not a snide remark, I am genuinely curious. An example would be nice, too.

Thanks.

>
> -- Jan Hidders
Received on Wed Sep 06 2006 - 23:58:54 CEST