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

From: David Cressey <cressey73_at_verizon.net>
Date: Thu, 22 Mar 2007 13:21:56 GMT
Message-ID: <UpvMh.15003$dG.1479@trndny08>

"Kevin Kirkpatrick" <kvnkrkptrck_at_gmail.com> wrote in message news:1174496967.312698.308660_at_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.
>

"resembles" is really "belongs to the same class as". The same problem exists not only for fingerprints, but also for floating point numbers that are subject to measurement error or computational error. Received on Thu Mar 22 2007 - 08:21:56 CDT