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

RE: URIs vs. URNs vs. URLs

From: Pierre-Antoine CHAMPIN <champin@bat710.univ-lyon1.fr>
Date: 07 Aug 2001 16:45:52 +0200
To: Patrick.Stickler@nokia.com
Cc: uri@w3.org, www-rdf-interest@w3.org
Message-Id: <997195553.2707.51.camel@lisiperso3>
On 06 Aug 2001 10:37:16 +0300, Patrick.Stickler@nokia.com wrote:
> 
> It's interesting to see this discussion arising again (as
> it did a few months back, and seemingly every few months
> for quite some time ;-)
> 
> The bottom line, as I see it, is that there are two things
> we need both for the Web and the Semantic Web: (1) names, 
> and (2) locations. That's the original logic between the 
> URL/URN distinction (no less reflected in the very terms 
> themselves). And this distinction is still crucial.

This is my understanding of the original RFCs about URLs and URNs.
But the fact is : the W3C officially denies that distinction,
see http://www.w3.org/DesignIssues/NameMyth.html

> What RDF must have are universal names. URI's were adopted
> (seemingly) because they offered an easy source for universal
> names which theoretically should not collide. Unfortunately,
> folks started to use HTTP URLs rather than some form
> of URN scheme

I also tend to agreed.
But the W3C says something different : "Cool URIs don't change"
see http://www.w3.org/Provider/Style/URI

Though:

> and all of the issues about persistency, authority, 
> ownership, control, transferral, responsibility, etc. etc. came up 
> because HTTP URLs are linked to DNS and thus inherit all such 
> management issues from DNS.

Heartfully agreed. TBL kind of addressed those problems
in http://www.w3.org/DesignIssues/PersistentDomains
but no official solution has been recomended AFAIK,
and wild URIs are still running.

> It also confused alot of folks into
> thinking that resource URIs should be dereferencable in some
> fashion

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'll take a trivial
example :

I have two ways of dereferencing the word "cat".
I can go to a pet shop and get one - the object.
I can look in a dictionnary and get a description of it.
On the other hand, I can only look at the dictionnary to dereference the
word "unicorn". This is because unicorns do not belong to my world.

This is the same with the Web.
Some things belong to it, like XML documents. I can get them as objects,
or description of them (metadata).
Some things  do not belong to the web, like books, persons. I can give
them a name, and dereference it to a description, but never to the
object.

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.

Furthermore, if we decide that the retrieved data is a decription of the
identified object rather than the object itself, then the retrieved data
needs another name. What would be the name of my homepage, of the W3C's
homepage, then ??

  Pierre-Antoine
Received on Thursday, 9 August 2001 10:03:45 GMT

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