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Re[2]: Summary: Section 2: What does a URI identify?

From: Chris Lilley <chris@w3.org>
Date: Mon, 18 Mar 2002 23:29:11 +0100
Message-ID: <2271340343.20020318232911@w3.org>
To: Paul Grosso <pgrosso@arbortext.com>
CC: "Jonathan Borden" <jonathan@openhealth.org>, www-tag@w3.org
On Monday, 18 March, 2002, 21:20:32, Paul wrote:

PG> At 14:55 2002 03 18 -0500, Jonathan Borden wrote:
>>I disagree. Again, particularly with RDF applications that do not
>>necessarily maintain the concept of a "current document", a bare fragment
>>identifier might be converted into an absolute URI + frag id, via the base
>>URI. Indeed RFC 2396 explicitly licences such use when appropriate.

PG> No!  People keep getting this wrong, and unfortunately major browsers
PG> do too which is really making a mess of the use of base URLs to the
PG> point where one cannot use <base> and <a href="#xxx"> sorts of references
PG> together, because this misinterpretation of #xxx refs with respect to
PG> base URL destroys the ability to maintain intradocument xrefs.

In connection with which, I was slightly startled to come across this
the other day (in the PRISM 1.1 spec, under changes from 1.0):

> Removed examples of use of xml:base

> In line with the recent decision from the RDF Core working group on
> the use of xml:base in RDF 1.0 descriptions[cite], PRISM has changed
> its advice to implementers. Where the 1.0 version stated that
> implementers should be cautious about using it, the 1.0.1 version
> states that creators of PRISM descriptions SHOULD NOT use it. The
> examples that did use it were changed.

Unfortunately the [cite] appears to be a placeholder and not an actual
link . I also note an RDF usage of RDF:about="" to mean 'the current
file' and I have seen usage (not in RDF) of xmlns:"" to mean "blow
off an existing namespace declaration and make unprefixed stuff in
this element be anonymous, not in any namespace" which broadly
translates to using the current document as the namespace. Or not...

> 2.3.1               A Brief Digression on Identifiers
> Note that the empty string is given as the value of the rdf:about
> attribute in Example 2. This means that the PRISM description is
> about the current file. The value of the rdf:about attribute is
> required to be a URI reference – either absolute or relative. By
> definition, relative URIs are relative to an absolute URI known as
> the base. By default, that base URI is the URI of the containing
> document. In this case, the relative URI reference is the empty
> string, meaning that it does not modify the base URI. Therefore, the
> rdf:about attribute refers to the current document.

> Similarly, Example 3 also shows the use of relative URIs. In this
> case they would be files in the same directory as the PRISM
> manifest.

> A new attribute, xml:base [W3C-XML-BASE], has been specified by the
> W3C to allow XML documents to explicitly set their base URI. At the
> time of this writing, it appears the RDF Core Working Group will
> update the RDF specification to allow that attribute. PRISM
> recommends that implementations SHOULD support the xml:base
> attribute.

Hmm so does RDF use, encourage, deprecate xml:base (or all of the
above depending on context)?
 http://www.prismstandard.org/techdev/prismspec11.asp
 
-- 
 Chris                            mailto:chris@w3.org
Received on Monday, 18 March 2002 17:31:04 GMT

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