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RE: URIs / URLs

From: Charles McCathieNevile <charles@w3.org>
Date: Thu, 12 Apr 2001 11:13:48 -0400 (EDT)
To: Lee Jonas <lee.jonas@cakehouse.co.uk>
cc: "'Aaron Swartz'" <aswartz@swartzfam.com>, RDF Interest <www-rdf-interest@w3.org>
Message-ID: <Pine.LNX.4.30.0104121108510.18863-100000@tux.w3.org>
No, you are falling into the trap I am describing, of making assertions about
a URI that you did not publish and for which you appear to be unaware of the
semantics.

As far as I am aware, mailto:charles@w3.org is a URI that W3C maintains,
whether ot provides a way to get to me, or just a way to get a mesage saying
that I have been sacked for eating all the vegemite.

At any rate, the semantics of that URI are the responsibility of the
publisher - in this case w3.org (and here we get to the real process problem
- the people who give away ^H^H^H^H^H sell domain names do not yet seem
convinced that they have any responsibility to the community that relies on
domain names to identify something). If we have a body that assigns URNs then
we just repeat the problem, plus we have to resolve them and for some reason
everyone seems to think that the best way of doing that is via a URI
identifier...

chaals


On Thu, 12 Apr 2001, Lee Jonas wrote:

  Charles McCathieNevile [mailto:charles@w3.org] 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
  this
  >resource at date XXXX are no longer valid, but do apply to resource YYYY" -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
  remain
  >stable is any better than a publisher of URIs making the same guarantee.
  The
  >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 mailto:veggiemite-beast@w3.org
  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 mailto:charles@w3.org, because you may
  leave and another Charles may take over your mailbox - it would be
  inappropriate to use mailto:charles@w3.org 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
  idea
  >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.

  regards

  Lee


  >cheers
  >
  >Chaals
  >
  >On Thu, 12 Apr 2001, Lee Jonas wrote:
  >
  >  >From what you say, use of URLs in RDF must be treated with extreme
  caution.
  >  Unless a publisher guarantees that they won't change the fundamental
  nature
  >  of the resource identified by a URL, you cannot rely on it to identify
  what
  >  you intend it to.
  >
  >  This seems like the most compelling argument for using URNs for
  identifying
  >  anything other than representation mappings yet!
  >
  >  regards
  >
  >  Lee
  >
  >
  >--
  >Charles McCathieNevile    http://www.w3.org/People/Charles  phone: +61 409
  134 136
  >W3C Web Accessibility Initiative     http://www.w3.org/WAI    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,
  France)


-- 
Charles McCathieNevile    http://www.w3.org/People/Charles  phone: +61 409 134 136
W3C Web Accessibility Initiative     http://www.w3.org/WAI    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, France)
Received on Thursday, 12 April 2001 11:13:52 GMT

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