Re: Objects and Relations

JOG wrote:
> On Feb 14, 8:08 am, "David BL" <davi..._at_iinet.net.au> wrote:
[...]

>
> Nevertheless, for the benefit of other readers if nothing else, let me
> state that Keith has hit the nail on the head.
>
> 1) Lego blocks are /not/ the same. They always have a different
> location attribute.
> 2) Hence their x,y,z position attribute always identifies them.
> 3) However this identifer is very hard to record and keep track of,
> even though it exists.
> 4) So we represent it with a surrogate identifer (which is hence just
> an 'untrackable' attribute or, as others refer to it, an unfamiliar
> attribute).
> 5) OID's are hence not needed, and everything is just a value, as it
> should be.

I've found this thread really interesting, especially since it took a turn towards this topic. I'd like some feedback as to whether I'm understanding your point - I think I am.

There seems to be some similarity between an OID (as I understand it) and a surrogate identifier as you describe it above.

Would I be correct in saying that all OIDs are surrogate identifiers, but that not all surrogate identifiers are OIDs?

In particular, it seems that the difference is that, given some entity which we would like to model:

(1) No two entities can share the same value for their surrogate identifier, BUT one entity can have two values for the surrogate identifier.

(2) No two entities can share the same OID, AND no entity can have two OIDs.

Cheers,
Joe Received on Thu Feb 15 2007 - 04:54:20 CET