# Re: foreign key constraint versus referential integrity constraint

From: Bob Badour <bbadour_at_pei.sympatico.ca>

Date: Wed, 28 Oct 2009 19:41:28 -0300

Message-ID: <4ae8c89a$0$26487$9a566e8b_at_news.aliant.net>

> That is a form of argument that I've seen quite often regarding various

Date: Wed, 28 Oct 2009 19:41:28 -0300

Message-ID: <4ae8c89a$0$26487$9a566e8b_at_news.aliant.net>

> 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.*Ahem.

> To try to answer that I would ask when do we ever record

*> "extensions" of arithmetic equations?
*

Whenever anyone writes the word "let":

> 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.
*

Whether involving numbers or no numbers, a relation is a relation. What we can do with relations doesn't change because some of them involve numbers and some of them do not. Received on Wed Oct 28 2009 - 23:41:28 CET