Re: Identity modelling

Gene Wirchenko wrote:
> x wrote:

>>David Cressey wrote:
>>
>>>One interesting case is that of the URL.
>>>Is a URL a key or a pointer?
>>>Does it name the resource, or does
>>>it locate the resource?
>>
>>It is a pointer, not a key.
>>The URL and the resource are not tied together.

The URL is just an alias for another locator. The existence of what is there (at the pointed-at) location does not depend on the existence of the URL.

Real keys do not have things that are existentially dependent on them, but my intuition (not checking any definitons anywhere) is that primary keys do: A tuple (relational value) can only exist /with/ it.

So, I (almost) agree with x:
the URL is a pointer(-alias), no key.

The distinction between pointer and reference is that the referenced object's physical location may change without a need to change the reference. The alias is one way (an indirection) to accomplish that.

So the URL may be a reference - but still no key.

My 2 Eurocents. Received on Tue Aug 30 2005 - 20:53:28 CEST