Re: Separate foreign keys with shared ID space
Date: Mon, 02 Aug 2004 02:39:49 GMT
Message-ID: <UPhPc.197024$%_6.162650_at_attbi_s01>
"Hans Forbrich" <forbrich_at_yahoo.net> wrote in message news:jZROc.2236$T_6.1453_at_edtnps89...
> Marshall Spight wrote:
>
> > "Christian Antognini" <christian.antognini_at_trivadis.com> wrote in message
> > news:410affcf$1_at_post.usenet.com...
> >>
> >> 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