# Re: foreign key constraint versus referential integrity constraint

From: paul c <toledobythesea_at_oohay.ac>

Date: Wed, 28 Oct 2009 22:57:15 GMT

Message-ID: <f%3Gm.50644$PH1.37179_at_edtnps82>

> Ahem.

> Whenever anyone writes the word "let":

> Whether involving numbers or no numbers, a relation is a relation. What

Date: Wed, 28 Oct 2009 22:57:15 GMT

Message-ID: <f%3Gm.50644$PH1.37179_at_edtnps82>

Bob Badour wrote:

> paul c wrote:

*>
*

>> 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.

*>**> x + y = 5 is a relation. z = x - 2y is a relation. They are linear**> polynomial functions, and all functions are relations.**>**> x*x + y*y + z*z - r*r = 0 is also a relation. It is a relation**> describing a sphere of radius r centered at the origin. It is also a**> polynomial. While it is not a function, it is a relation.**>**>*>> To try to answer that I would ask when do we ever record "extensions" >> of arithmetic equations?

*>*> Whenever anyone writes the word "let":

*>**> Let u = x-3, v=y+2, w=z-1...**>**>*>> 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.*