Subject: Re: question about which column(s) are the right foreign key
From: Markus Bertheau <twanger@bluetwanger.de>
To: Josh Berkus <josh@agliodbs.com>
Cc: pgsql-sql@postgresql.org
In-Reply-To: <200406202157.57676.josh@agliodbs.com>
References: <1087766532.2660.27.camel@teetnang>
	<200406202157.57676.josh@agliodbs.com>
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Date: Fri, 25 Jun 2004 16:18:01 +0200
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=D0=92 =D0=9F=D0=BD=D0=B4, 21.06.2004, =D0=B2 06:57, Josh Berkus =D0=BF=D0=
=B8=D1=88=D0=B5=D1=82:
> Markus,
>=20
> > I have objects in my database, and they have an object id generated with
> > a sequence. Then I have object versions. The ids of object versions need
> > to be unique only within one object id. But for simplicity they're
> > generated with a sequence, too.
> >
> > Now I want to reference an object version. I can use just the object
> > version id, because it "happens" to be globally unique. Conceptually
> > though, I should use the object's id and its version's id.
> >
> > Now redundancy is Not Good=E2=84=A2, so I wonder which way is the Right=
 One=E2=84=A2.
> >
>=20
> Well, conceptually, you should have generated a numerical version id for =
each=20
> object version which would have told you the sequence in which that versi=
on=20
> was created, i.e. version #1 of object 23421, version #2 of object 23421,=
=20
> etc.  This can be automated a number of ways, although it does require=20
> locking the object during a version save.
>=20
> The problem with the setup you have now is that you have an Object ID, wh=
ich=20
> doesn't intrinsically mean anything, and an Object Version ID, which also=
=20
> doesn't tell you anything about the object or the version.   If you want =
to=20
> keep information about which "edition" of an object this particular=20
> object-version is, you'll have to add a column -- which will then make th=
e=20
> object-version id redundant, since the table will then have two keys.
>=20
> That's "the Right One=E2=84=A2"

Thanks. That really did provide the neccessary insight.

--=20
Markus Bertheau <twanger@bluetwanger.de>