Re: More on identifiers

On Jun 5, 2:25 am, "Walter Mitty" <wami..._at_verizon.net> wrote:
> "David BL" <davi..._at_iinet.net.au> wrote in message
>
> news:03132046-3fd2-4bb1-9e00-cd81ece451c2_at_h2g2000yqg.googlegroups.com...
>
>
>
> > Informally I think of abstract identifiers as "internal glue" within a
> > relational database.  A bit more formally, they are characterised as
> > identifiers that could be mapped bijectively to different values
> > throughout the database without changing the recorded information.
> > One would therefore hope that they aren't visible to end users.
>
> > I have wondered for some time whether abstract identifiers are only
> > needed within the confines of a flat relational model.  The following
> > hypothetical example is meant to cast some light on this question.
> > I'm hoping you'll see the underlying matters of principle and see how
> > it raises some interesting questions and ideas:
>
> > Let a cardboard box of items land on your desk and your task is to
> > record information about the items in a database.  In theory each item
> > is uniquely identified by its (x,y,z) position at any given epoch.
> > However, the idea is that the items are mixed up in the box and their
> > positions are irrelevant to the information that needs to be recorded.
>
> > The items are not labelled.  The idea is to uniquely identify them
> > (only) by their observable properties.  This is indeed assumed to be
> > an important integrity constraint to be enforced by the DBMS.  Note as
> > well that it would be upsetting (and potentially very costly or
> > impractical) if the database system forces items to be labelled when
> > there shouldn't be a need to.
>
> Consider two electrons.  They both have the same mass, and they have the
> same charge.  They might have opposite spins.  But the minute we add a third
> electron, the spin of two of them is going to be identical.  

Is there anything QM specific about it? Consider 3 coins on the table. 2 of them have identical states (head-head or tail-tail) Received on Sat Jun 06 2009 - 00:06:48 CEST