Re: One-To-One Relationships
Date: Sat, 01 Dec 2007 18:37:17 -0400
>>>Entities are figments of our imaginations. >> >>Heh. So are relations, attributes, values, and domains. >>So are rectangles, straight lines, points, and angles. >>So are "real" numbers, functions, and differential equations. >>But they all work pretty well.
We do not pretend that relations are real or are part of the universe of discourse -- with the notable exception of the system catalog, of course. Relations make no imagined and unecessary distinctions. They are merely a structure and operations useful for symbolic manipulation.
Fictitious distinctions increase complexity without any compensating benefit.
>>We're dealing with conceptual modelling here. >>I prefer the term 'modelling constructs', if you don't mind. >> >>I agree with Chen (and e.g. OO design, which takes it to another extreme) >>that a notion of entity is natural, unproblematic and well worth having. >> >>You apparently disagree. Make me understand why. Be specific.
I already was specific, and the idiot accused me of having a trantrum for my specificity.
> I know you weren't asking me, but my question about the
> whole entities thing is, what do they buy me? I mean,
> I already have this concept of "relation" which seems to
> be powerful enough to be considered a foundation for
> more or less all of mathematics. What *new* capability
> is introduced by having a different thing called "entity?"
> Why can't I just write down relations?
Indeed. Or predicates is another good option, which amounts to the same.
> If I don't have them fully modeled yet, I don't see how
> the identity question is any issue. I know every relation
> will have *some* key. If I need to reference a specific
> member of relation B from relation A, I know it will be
> possible to have an attribute in A that is a key of relation
> B. If I just call it BId for the moment, what is the problem?
> If I later discover that B has a compound key, then that's
> fine too.
> My end product is a schema for relations. Why don't I just
> model using those? Why not cut out the middle man?
Received on Sat Dec 01 2007 - 23:37:17 CET