"paul c" <toledobythesea_at_oohay.ac> wrote in message
news:JQ94i.200044$DE1.108062_at_pd7urf2no...
>
> I've never seen anybody justify why a foreign key must be a candidate key
> in the referenced relation/relvar/table except for 'so-and-so says so'.
> Whereas I've seen examples where the non-key reference is essential.
I think the main answer is "history". As I see it there is no real
restriction. The term "foreign key" is merely a shorthand or syntactical
device meaning the type of constraint you described. That does not preclude
other types of constraints - it's just that by convention they are not
"foreign keys".
--
David Portas
Received on Mon May 21 2007 - 01:04:53 CDT
