Re: foreign key constraint versus referential integrity constraint
Date: Wed, 28 Oct 2009 19:41:28 -0300
> 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.
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.
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.> "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
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