Re: Relation Schemata vs. Relation Variables
Date: 6 Sep 2006 07:53:39 -0700
Message-ID: <1157554419.796440.287750_at_e3g2000cwe.googlegroups.com>
Bob Badour wrote:
> JOG wrote:
> > Brian Selzer wrote:
> >
> >>"Jan Hidders" <hidders_at_gmail.com> wrote in message
> >>news:1157532864.768886.10750_at_d34g2000cwd.googlegroups.com...
> >>
> >>>Brian Selzer wrote:
> >>>
> >>>>"Jan Hidders" <hidders_at_gmail.com> wrote in message
> >>>>news:1157457516.222077.154380_at_b28g2000cwb.googlegroups.com...
> >>>>
> >>>>>Sets of facts can and do change, and transitional constraints restrict
> >>>>>wich transitions from one set of fact to another are allowed. I don't
> >>>>>see a fundamental problem here. Note btw. that they are a strict
> >>>>>subclass of the restrictions that might be expressed by some kind of
> >>>>>temporal logic.
> >>>>
> >>>>I don't understand what you mean. Are you saying that transition
> >>>>constraints can be expressed as state constraints?
> >>>
> >>>A transitional constraint is a binary predicate over states. One
> >>>argument is the old state and the other the new state. Or, put in
> >>>another way, a transition constraint constrains the transitions. This,
> >>>I would say, is pretty much the definition of the term.
> >>>
> >>>Or did I misunderstand your question and are you asking about temporal
> >>>logics?
> >>>
> >>
> >>No. I just wanted to be sure that we're on the same page.
> >>
> >>The point that I was making in the original post is that because keys can
> >>change, there isn't enough information given only the old state and the new
> >>state to pair up the values in the old state with those in the new state for
> >>comparison.
> >
> > You cannot pair up values David. You can only compare the sets as a
> > whole.
>
> I think you misspoke. I draw your attention yet again to Date's
> _Principle of Incoherence_: "It is very difficult to respond coherently
> to that which is incoherent."
guilty as charged. Very difficult indeed. I'll rephrase:
There is no transition between individual tuples in different relation values Brian, and it is illogical to try and compare them as if there were. There is only a transition from one set of tuples to another, as a whole. (This is because, as a variable, a relvar posesses an identity outside of its current value).
>
> One can pair up values any number of ways: least, greatest, lesser,
> greater, least greater, greatest lesser etc.
>
> Cartesian product and restrict have the effect that one can pair up
> tuples within relations ie. elements within sets.
Received on Wed Sep 06 2006 - 16:53:39 CEST