Re: Separate foreign keys with shared ID space

From: Marshall Spight <>
Date: Mon, 02 Aug 2004 02:39:49 GMT
Message-ID: <UPhPc.197024$%_6.162650_at_attbi_s01>

"Hans Forbrich" <> wrote in message news:jZROc.2236$T_6.1453_at_edtnps89...
> Marshall Spight wrote:
> > "Christian Antognini" <> wrote in message
> > news:410affcf$
> >>
> >> A PK should have no business meaning.
> >
> > Says who? Can you justify this statement?
> A PK should be selected to uniquely identify an entity. Ideally, and by
> formal definition, the PK is invariant.

Whose formal definition? Relations are sets; the only formal definitions I'm aware of are those of set theory. Set theory does not have "primary keys" in it; only candidate keys. Set theory doesn't say anything about sets being invariant. And keys aren't "selected" to be unique; they are unique or they aren't keys. Every set must have at least one key.

Marshall Received on Mon Aug 02 2004 - 04:39:49 CEST

Original text of this message