Re: One-To-One Relationships

On Dec 1, 8:52 am, rp..._at_pcwin518.campus.tue.nl (rpost) wrote:
>
> >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.

Agreed.

> 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 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?

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?

http://dictionary.reference.com/search?q=disintermediation

Marshall Received on Sat Dec 01 2007 - 16:20:29 CST