Charles McCathieNevile [] wrote:

>Yes, I assert that it is risky to make statements about something when you
>don't know how good your identifier is. (Although it is possible to state
>that "I think this resource might disappear", or "statements made about
>resource at date XXXX are no longer valid, but do apply to resource YYYY" -
>the latter is one of the things I am trying to work out how to do in EARL,
>where we need to do it for  different reasons)
>But I don't understand how a publisher of URNs guaranteeing that they
>stable is any better than a publisher of URIs making the same guarantee.
>problem to be solved is a human one, not a technical one, as I see it.

Of course, on this you are entirely correct.  Stable URNs are no better than
stable URLs for identifying resources. 

But, from your earlier post, the URL
identifies the person at the W3C that eats the most veggiemite.  The URL can
remain stable, whilst being updated daily to reflect the person at the W3C
who ate the most veggiemite that day.

If you want to make RDF assertions on that basis then this URL is the most
appropriate identifier.

However, if one wants to make assertions about Charles Cavendish
McCathieNevile, they shouldn't use, because you may
leave and another Charles may take over your mailbox - it would be
inappropriate to use unless you were making assertions
about the owner of the charles mailbox at W3C.

This can be generalised to all URLs where the publisher does not explicitly
state that they will never change the resources represented.

Instead of using an identifier to locate Charles Cavendish McCathieNevile as
the owner of the "charles" mailbox at W3C, it would be better to assign you
a globally unique identifier (e.g. a UUID) that will still identify you
after you leave the W3C, and make assertions about you via that identifier.

>From another perspective, the semantic web seems like a very good use case
>that encourages publishers of URIs not to break them. Thereby making the
>of introducing URNs less and less interesting...

The use of URNs is not to overcome stability of URLs but to overcome
transience in the resources they represent.  The semantic web might be more
likely to make assertions about resources that are not intended to be
electronically accessible, like Charles Cavendish McCathieNevile, meaning
that the need for URNs increases, not diminishes.



>On Thu, 12 Apr 2001, Lee Jonas wrote:
>  >From what you say, use of URLs in RDF must be treated with extreme
>  Unless a publisher guarantees that they won't change the fundamental
>  of the resource identified by a URL, you cannot rely on it to identify
>  you intend it to.
>  This seems like the most compelling argument for using URNs for
>  anything other than representation mappings yet!
>  regards
>  Lee
>Charles McCathieNevile  phone: +61 409
134 136
>W3C Web Accessibility Initiative    fax: +1 617
258 5999
>Location: 21 Mitchell street FOOTSCRAY Vic 3011, Australia
>(or W3C INRIA, Route des Lucioles, BP 93, 06902 Sophia Antipolis Cedex,

Received on Thursday, 12 April 2001 10:23:53 UTC