W3C home > Mailing lists > Public > uri@w3.org > September 2001

Re: Excess URI schemes considered harmful

From: Michael Mealling <michael@neonym.net>
Date: Wed, 26 Sep 2001 13:58:17 -0400
To: Mark Baker <distobj@acm.org>
Cc: michael@neonym.net, Rob Lanphier <robla@real.com>, uri@w3.org
Message-ID: <20010926135817.B13022@bailey.dscga.com>
On Wed, Sep 26, 2001 at 11:59:44AM -0400, Mark Baker wrote:
> > On Tue, Sep 25, 2001 at 02:52:50PM -0400, Mark Baker wrote:
> > > There's different degrees of equivalency at play here.
> > > 
> > > It is the case that if two HTTP URIs are equal, that they necessarily identify
> > > the same resource (also see RFC 2616 sec 3.2.3).  It is not the case that if 
> > > two HTTP URIs are *not* equivalent (even modulo 2616/3.2.3), that they do 
> > > *not* represent the same resource.  The only way to determine whether two 
> > > non equivalent HTTP URI represent the same resource latter is to have 
> > > authoritative info about that equivalence (or lack thereof).  One way for 
> > > that authoritative info to be communicated is with an HTTP redirect.
> > > 
> > > Even the current CTURI draft has the latter problem, as the encoding is not
> > > canonical.
> > 
> > This is indeed the case with _all_ URIs. Equivalence of resources across 
> > schemes is iff the URIs are lexicographically equal.
> 
> Untrue.  See below.
> 
> > URIs themselves
> > express no other type of equivalence other than that since equivalence
> > is always application specific and more often than not is also context
> > specific. Unless you have some application specific knowledge talking
> > about equivalence of Resources is a very dangerous and, IMNSHO, simply
> > a Bad Thing To Do...
> 
> Luckily, HTTP is an application protocol, so is in a very good position
> to define application specific knowledge/context, such as when http
> URIs are "equivalent" or not.  Non-http URI schemes don't have that
> advantage.

Right. How does that negate my assertion that URIs in and of themselves
don't discuss equivalence of Resources outside lexical equivalence of
the URIs that identify them?

> IMO, yet another reason why using http URIs is Goodness.

and IMHO, yet another reason why HTTP semantics are not applicable across
all URI schemes. HTTP's concept of equivalence is IMHO, fairly infantile.
The equivalence semantics that something like RDF gives you are much
more interesting and useful. but again, even the semantics that RDF
gives you may not be useful for other applications such as directory 
services, network management, monitoring, rights management, etc...

-MM

-- 
--------------------------------------------------------------------------------
Michael Mealling	|      Vote Libertarian!       | urn:pin:1
michael@neonym.net      |                              | http://www.neonym.net
Received on Wednesday, 26 September 2001 14:04:41 UTC

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