Path: news.cambrium.nl!textnews.cambrium.nl!feeder2.cambriumusenet.nl!feed.tweaknews.nl!217.73.144.44.MISMATCH!feeder.ecngs.de!ecngs!feeder2.ecngs.de!212.27.60.7.MISMATCH!feeder1-1.proxad.net!proxad.net!feeder1-2.proxad.net!74.125.46.134.MISMATCH!postnews.google.com!e24g2000vbe.googlegroups.com!not-for-mail From: Tegiri Nenashi Newsgroups: comp.databases.theory Subject: Re: More on identifiers Date: Fri, 5 Jun 2009 15:06:48 -0700 (PDT) Organization: http://groups.google.com Lines: 42 Message-ID: <8534e0d3-9d75-48f8-a43f-0c16e576ed85@e24g2000vbe.googlegroups.com> References: <03132046-3fd2-4bb1-9e00-cd81ece451c2@h2g2000yqg.googlegroups.com> NNTP-Posting-Host: 148.87.1.172 Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable X-Trace: posting.google.com 1244239608 24355 127.0.0.1 (5 Jun 2009 22:06:48 GMT) X-Complaints-To: groups-abuse@google.com NNTP-Posting-Date: Fri, 5 Jun 2009 22:06:48 +0000 (UTC) Complaints-To: groups-abuse@google.com Injection-Info: e24g2000vbe.googlegroups.com; posting-host=148.87.1.172; posting-account=PBsn8woAAADaWofLEAjNrE17YVrUmBlm User-Agent: G2/1.0 X-HTTP-UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.0.5) Gecko/2008120122 Firefox/3.0.5,gzip(gfe),gzip(gfe) Xref: news.cambrium.nl On Jun 5, 2:25=A0am, "Walter Mitty" wrote: > "David BL" wrote in message > > news:03132046-3fd2-4bb1-9e00-cd81ece451c2@h2g2000yqg.googlegroups.com... > > > > > Informally I think of abstract identifiers as "internal glue" within a > > relational database. =A0A 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. =A0The 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. =A0In theory each ite= m > > 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. =A0The idea is to uniquely identify them > > (only) by their observable properties. =A0This is indeed assumed to be > > an important integrity constraint to be enforced by the DBMS. =A0Note a= s > > 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. =A0They both have the same mass, and they have th= e > same charge. =A0They might have opposite spins. =A0But the minute we add = a third > electron, the spin of two of them is going to be identical. =A0 Is there anything QM specific about it? Consider 3 coins on the table. 2 of them have identical states (head-head or tail-tail)