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Home -> Community -> Usenet -> comp.databases.theory -> Re: Negative Numbers in "Identity" or" Autonumber" fields

Re: Negative Numbers in "Identity" or" Autonumber" fields

From: Kevin Kirkpatrick <kvnkrkptrck_at_gmail.com>
Date: 21 Mar 2007 10:09:27 -0700
Message-ID: <1174496967.312698.308660@o5g2000hsb.googlegroups.com>


On Mar 21, 11:38 am, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
> Marshall wrote:
> > On Mar 21, 8:28 am, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
>
> >>Marshall wrote:
>
> >>>On Mar 21, 4:00 am, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
>
> >>>>Marshall wrote:
>
> >>>>>On Mar 20, 10:31 am, "JOG" <j..._at_cs.nott.ac.uk> wrote:
>
> >>>>>>[...] Nothing in a
> >>>>>>proposition should ever be hidden from the user. Propositions come
>
> >>>>>>from outside of the logical layer after all. If an attribute is an
>
> >>>>>>identifier then it clearly impacts on identifying items in the real
> >>>>>>world.
>
> >>>>>I buy the "nothing should be hidden" argument, but I can't
> >>>>>decide if a domain that only supports equality is hiding
> >>>>>anything or not.
>
> >>>>It has to have at least one possible representation.
>
> >>>Can you elaborate? Why does it need at least one?
> >>>What breaks if it doesn't?
>
> >>How does one express any literal without at least one possible
> >>representation?
>
> > Okay, sure, yes, that's a point. But that's more of a structural
> > objection than a functional one. What breaks if a type doesn't
> > have literals?
>
> The basic ability to specify a value.
>
> What about the model requires literals?
>
> A model for expressing values has to have a way to express them. I don't
> think I understand your question.
>
> > In the case of equality, I can point to what exactly breaks if
> > a type doesn't support it: join. Specifically equijoin requires
> > some kind of "equi-".
>
> > What breaks if a type doesn't have literals?
>
> Everything.
>
>
>
> > I'm not particularly attached to this construct, but if it is
> > flawed I'd like to be able to put my finger right on it.- Hide quoted text -
>
> - Show quoted text -- Hide quoted text -
>
> - Show quoted text -

Assignment is obvious (and assignment implies representation)... I've always wondered about the need for "equality". Consider "fingerprint_scan" a domain in which the only means for comparison of two fingerprint_scan values is "resembles(F1, F2, points_to_match)". As such, equality is not defined and F1=F2 should be considered meaningless. Does this really break anything in the relational model - after all, I can still do theta joins, just not equijoins. Received on Wed Mar 21 2007 - 12:09:27 CDT

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