W3C home > Mailing lists > Public > www-rdf-interest@w3.org > August 2001

RE: URIs vs. URNs vs. URLs

From: <Patrick.Stickler@nokia.com>
Date: Wed, 8 Aug 2001 10:54:19 +0300
Message-ID: <2BF0AD29BC31FE46B78877321144043114BF74@trebe003.NOE.Nokia.com>
To: champin@bat710.univ-lyon1.fr
Cc: uri@w3.org, www-rdf-interest@w3.org
> In my opinion, the confusion is about *what* should be dereferenced.
> Sometimes it is the named object, sometimes it is a 
> *description* of it.
> Those are definitely different in my opinion. 

I fully agree. But they are also different from name versus location.

> I'll take a trivial
> example :
> ...
> Dereferencing http URIs with the HTTP protocol means for many people
> "getting the actual object", like going to the pet shop, *not* looking
> in the dictionnary. Using it the other way *is* confusing -- like
> deciding that my homepage URL identifies myself, or http://www.w3.org/
> identifies the W3 consortiom.

Good examples. 

Really, we have three different things going on here that I can see: 

(1) names versus locations

(2) concepts versus various realizations of concepts (treating
    both the actual cat and a description of the cat as types of 
    realizations of the shared concept of that cat)

(3) characteristics of specific URI schemes (management, intended
    usage, inherent semantics, persistence of access, persistence 
    of uniqueness, etc.) used for universal identifiers

* Names may resolve to zero or more locations. 
* Locations resolve (dereference) to data content. Whether that data is a 
  description of a thing or the thing itself is a separate issue.
* URIs are used to provide identity to both names and locations. 

The original URN/URL distinction addressed #1 above, but seems to have 
been abandoned. Current URI definitions make no distinction whatsoever 
between instances of #2. Issues relating to #3 are practical in nature
and are addressable irrespective of #1 and #2. Thus, in a way, the
present discussion is actually outside the scope of and irrellevant
to the (apparent) original issue of this thread -- namely the suitability
of some URI schemes as reliably persistent and unambiguous universal
identifiers ;-)  Still, because the three issues above are *not* clear
in the URI/RDF/SW literature, these discussions continue to merge.

A generalized approach to addressing the above issues might be to define 
an ontology both for URL/URN type distinctions as well as for realization 
distinctions (instance vs description) -- possibly even a taxonomy
of common URI semantics in general.

XTM addresses the first two issues to a certain degree, but blurs their



Patrick Stickler                      Phone:  +358 3 356 0209
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Received on Thursday, 9 August 2001 08:41:49 UTC

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