RE: URIs / URLs

Charles McCathieNevile [mailto:charles@w3.org] wrote:
>On Thu, 12 Apr 2001, Lee Jonas wrote:
>[snip]
>  If Pierre-Antoine leaves example.edu and is replaced by Jean-Claude
Champin,
>  who puts his home page in the same place at 'http://example.edu/~champin'
>  then not only has the representation (html doc) changed, but the same
>  location ('http://example.edu/~champin') now identifies Jean-Claude (or
>  Jean-Claude's conceptual home page, etc).
>
>  I.e. the same URI identifier has changed from identifying Pierre-Antoine
to
>  identifying Jean-Claude (or repective home pages, etc).
>
>  Taking 'http://example.edu/~champin/' to identify "the person named
Champin
>  currently enrolled at Example University" as you said above implies that
>  URLs do not identify these resources through representations, but
identify
>  mappings-to-resources through representations instead.  This would have
very
>  serious ramifications for RDF.
>
>  Regardless of the interpretation of Resource, doesn't it strike you as a
>  major blow to writing metadata statements about URLs that remain correct
>  over time?  Consider making assertions about Pierre-Antoine only to find
3
>  months later that those assertions are are actually making (probably
false)
>  statements about Jean-Claude instead.
>
>No, it strikes me as a major blow to the Web if someone makes an assertion
>that is about Pierre-Antoine, but expresses it as being about "the person
>enrolled whose surname is Champin", and then expects the rest of the web to
>understand the implicit logic leap that their statement is about the
current
>referrent at the time of the statement and not the actual thing identified
>(i.e. the confusion between an idea and an instance).
>
>W3C says that it won't change a URI that begins http://www.w3.org/xxxx/
where
>xxxx is a year identifed in the "Common Era" (what used to be called years
>anno domini). So if W3C uses one such URI to identify me, and another to
>identify the staff contact for the authoring tool guidelines working group,
>and another to identify the team member who eats the most vegemite, someone
>who wants to make an assertion about me should use the correct identifier.
>Likewise to talk say something about whoever eats the most vegemite (for
>example, that nobody is likely to steal their toast), it makes sense to use
>the correct URI, and not just assume that that will be me for ever.
>
>cheers
>
>Charles

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

Received on Thursday, 12 April 2001 09:17:53 UTC