# Re: foreign key constraint versus referential integrity constraint

Date: Wed, 28 Oct 2009 20:46:31 GMT

Message-ID: <H42Gm.50625$PH1.3205_at_edtnps82>

Tegiri Nenashi wrote:

...

> Is view definition a constraint? IMO it's purely terminological

*> matter. Consider relations x and y defined by some algebraic
**> identities. Is adding new view z (as a function of x and y) adding a
**> constraint to the system?
**>
**> Let's analyze a simpler example. Consider two real values constrained
**> by the equality:
**>
**> x + y = 5
**>
**> Is introducing a new variable z, say
**>
**> z = x - 2y
**>
**> a new constraint imposed onto the system? Not really, because,
**> variable z is redundant and can be eliminated, and it doesn't affect
**> the formal property of the system of being under constrained.
*

That is a form of argument that I've seen quite often regarding various RM questions, not just this one. I'd have no problem with it were it not called an "example". Since it is about arithmetic, it's at best a mere analogy to relations and we need to decide whether the analogy should apply. To try to answer that I would ask when do we ever record "extensions" of arithmetic equations? In other words, just because we have abstract operations for both numbers and relations doesn't mean one should mimic the other. If that's so, maybe somebody else can put it better. Received on Wed Oct 28 2009 - 21:46:31 CET