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Re: URIs vs. URIviews (was: Agenda for RDFCore WG Telecon 2002-02-15)

From: Dan Connolly <connolly@w3.org>
Date: 14 Feb 2002 22:29:42 -0600
To: Aaron Swartz <me@aaronsw.com>
Cc: RDF Core <w3c-rdfcore-wg@w3.org>
Message-Id: <1013747382.19333.31.camel@dirk>
On Thu, 2002-02-14 at 20:26, Aaron Swartz wrote:
> On 2002-02-14 3:08 PM, "Dan Connolly" <connolly@w3.org> wrote:
> 
> >> I really can't agree with this. It's our problem that RDF uses this
> >> non-standard piece of Web architecture, and in doing so has incurred all
> >> sorts of problems. If we're going to be the Resource Description Framework,
> >> we need we're actually describing resources. My ideal resolution would look
> >> like:
> >> 
> >>  o The WG resolves that the use of absolute URIs with fragment IDs is a
> >>    to identify Web resources is relatively incompatible with current Web
> >>    architecture.
> > 
> > ?????
> > 
> > Er.. it's the very heart of web architecture:
> > 
> > The principle that anything, absolutely anything, "on the Web"
> > should identified distinctly by an otherwise opaque string
> > of characters (A URI and possibly a fragment identifier) is
> > core to the universality.
> > 
> > -- http://www.w3.org/DesignIssues/Architecture
> 
> RFC2396 would agree with you except for the "and possibly a fragment
> identifier" bit.

RFC2396 does not say that a URI+fragid does not identify anything.
RFC2396 is silent on what a URI+fragid identifies.

> Same with Roy Fielding's dissertation (which clearly
> explains the reasons why this was an explicity design decision)

I was there, and I don't think it was an explicit design decision;
it was consensus by exhaustion. The software for URIs
handles fragment identifiers. The specs are a little more conservative,
but not inconsistent.

> and probably
> the many people who have invested in URI syntax, and don't want to go back
> and fix their HTTP clients, proxies, servers or other software (and maybe
> hardware) to support this addition of fragment identifiers.

All the software works with fragment IDs today. It has since 1989
or so.


> >>  o We recommend that RDF users refrain from using '#' in their Resource
> >>    identifiers and namespaces. RDF developers and tool creators may present
> >>    a warning to the user when using resource identifiers with '#' in them.
> > 
> > Why? rdf:type has a # in it, after all. How can they avoid it?
> > Why would they?
> 
> Perhaps I wasn't clear. I meant ones that they were creating (like if I
> wanted to come up with a namespace for my new vocabulary set, or my poodle).
>  
> > I don't see any explanation of a problem here.
> 
> We've discussed it several times on and off list, but I could reitierate it
> for you. The issue is that:
> 
> a) In the REST architectural model (which the TAG seems to be agreeing
> about) fragment identifiers only make sense within the context of an HTTP
> response (a bag of bits).

I disagree: a URI with a fragment makes sense as an identifier
in the global scope of the web.

> They identify parts of a document, not general
> Resources like full URIs.

A part of a document is 'something with identity', i.e. a resource.

> b) Deployed code doesn't support fragment identifiers as first-class objects

yes, it does.

> -- I can't ask an HTTP proxy about them, I can't query an HTTP server about
> them, etc.

Why would you expect to be able to? That's not how they work.

> And this is by design...
> 
> <MikeM> fragmetns are client side thing.....
>  - in #rdfig
> 
> Exactly! RDF has created this problem by taking what in Web Architecture is
> designed to be a client-side thing, the last step of resolution. TimBL
> explained this at the first W3C technical plenary: "[an HTTP client] puts
> the fragment ID in its pocket".

Yes, and how is that a problem?

> Also, in his Axioms of Web Architecture: The Web Model[1], Tim explains how
> a client holds on to the fragment ID so that it can pass it to the
> presentation object.
> 
> [1] http://www.w3.org/DesignIssues/Model
> 
> He's even got a nice diagram to explain it. I'm not sure how much clearer it
> can be that a fragment only makes sense in the context of presenting a
> document.

Yes, a fragment identifier is qualified by the stuff before
the #. That's how it works. How is that inconsistent with
RDF?

> >>  b) maintaining backwards-compatibility but
> >>  c) lay the ground work for future WGs to fix this bug
> > What bug?
> 
> The bug that RDF is incompatible with Web Architecture, as explained above.

I still don't see the bug.

Can you give a specific example of a failure mode?

> <MikeM> seriously, RDF's use of frags has caused so many problems.. If RDF
> needs something like it that badly then make it a new URI scheme that does
> it _right_
> 
> -- 
> [ "Aaron Swartz" ; <mailto:me@aaronsw.com> ; <http://www.aaronsw.com/> ]
-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Thursday, 14 February 2002 23:29:16 EST

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