Re: foreign key constraint versus referential integrity constraint
From: paul c <toledobythesea_at_oohay.ac>
Date: Wed, 28 Oct 2009 23:53:47 GMT
Message-ID: <fQ4Gm.50652$PH1.1101_at_edtnps82>
>
> That's very good, accurate up to a point and no argument except for a
> couple of things i) when he mentioned "variable" Tegiri didn't make it
> clear whether he was talking about one of Codd's non-binary relations, I
> presume traditional math philosophy would have to have some recasting
> for that (don't ask me how!) ii) even if I'm wrong about i), Codd's
> relations are slightly different in usage both because they use
> different operators than the arithmetic ones and because we can 'bend'
> the relational ops to produce a certainty from an uncertainty, notably
> when we use union to 'insert' to a relation - this seems quite different
> to me from what arithmetic allows.
Date: Wed, 28 Oct 2009 23:53:47 GMT
Message-ID: <fQ4Gm.50652$PH1.1101_at_edtnps82>
paul c wrote:
> 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.
>
> That's very good, accurate up to a point and no argument except for a
> couple of things i) when he mentioned "variable" Tegiri didn't make it
> clear whether he was talking about one of Codd's non-binary relations, I
> presume traditional math philosophy would have to have some recasting
> for that (don't ask me how!) ii) even if I'm wrong about i), Codd's
> relations are slightly different in usage both because they use
> different operators than the arithmetic ones and because we can 'bend'
> the relational ops to produce a certainty from an uncertainty, notably
> when we use union to 'insert' to a relation - this seems quite different
> to me from what arithmetic allows.
(Not to discount Bob B's reply - I may be stepping over some unmarked line in the above, which would make it a provocation but I often find those useful for seeing things more clearly.) Received on Thu Oct 29 2009 - 00:53:47 CET