Re: the two questions

"JOG" <jog_at_cs.nott.ac.uk> wrote in message news:0c832d02-88f5-495c-ab2b-8098afcd8818_at_d21g2000prf.googlegroups.com...
> On Nov 27, 3:49 pm, "Brian Selzer" <br..._at_selzer-software.com> wrote:
> > "JOG" <j..._at_cs.nott.ac.uk> wrote in message
> > Each individual that existed, exists, or can exist has a property that
> > distinguishes it from all other individuals that existed, exist or can
> > exist; so, yes, there is a property that the caterpillar and butterfly
> > share.
>
> Great, we have agreement :)
>
> > The problem is: I don't think haecceity can be observed directly.
>
> This time I agree with you (although I did have to look up what
> 'haeccity' meant) - it is often the case that the identifier we need
> isn't available to us (I mean we can't often check a butterflies dna
> right...).
>
> But we have to find a solution to this in the real world right - If I
> have a butterfly, how do I know it came from the caterpillar from
> earlier? Would you agree there are two options?
>
> 1) Check an identifier that we can manage to observe (dna if we're
> lucky, more likely the jar number we've kept it in, etc.)
> 2) If we couldn't access that identifier (or it was just too much of a
> pain to do so), we'd have needed to invent a new identifier as a
> replacement, that was trackable (a representative identifer for the
> insect's 'haeccity' - similar to what biologists do when they 'tag'
> birds).
>
> Again, all in the real world, before we get to a database.
>
> > If one were able to examine the history of the butterfly, one should be
able
> > to determine that it coincides with the history of the caterpillar--up
to
> > the point of the initial snapshot. The problem is: I don't think
history
> > can appear in a snapshot.
>
> I get your gist here but hope we can come back to it after you've
> looked at the above question. Regards, J.
>

As a practical matter, what we do when we want to track individual living creatures is to tag them. Let's take birds, rather than butterflies. Near where I live, they are banding birds. When a dead bird is found, they ask for the number from the band, if there is one. Among other things, this allows better tracking of bird flu.

A few days ago some people, in jest, suggested that people get an ID tattoed to their butt. For purposes of this discussion, banding birds is precisely the same concept, minus the humor. The number on the band identifies the band. Since the band is an artifact, we can build it so as to carry its identity around in visible form.

 Using the band number as if it were a bird number depends on attaching the band to the bird in a relatively permanent way. I think it's fair to call a band number an "artificial key". I'm less sure about the term "synthetic key". I think it's misleading to call it a "surrogate key". Surrogate for what?

We do the same thing when we use Social Security Number to identify people. In the narrowest sense, a SSN identifies an account in the Social Security system. The attachment between the person and the account is less tangible than the band on the bird, but is intended to be quasi permanent.

Again, all of this is "real world" before anything goes into a database. Received on Tue Nov 27 2007 - 18:13:07 CET