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encoding of URI references in RDF/XML (was Re: character encoding in RDF (including some new related issues))

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Thu, 06 Nov 2003 14:46:10 -0500 (EST)
Message-Id: <20031106.144610.74187836.pfps@research.bell-labs.com>
To: dave.beckett@bristol.ac.uk
Cc: www-rdf-comments@w3.org

> > I also worry about the details of espacing in URI references in RDF/XML.
> > My understanding is that URI references are supposed to be in escaped form,
> > and that downstream applications are not supposed to perform escaping,
> > except perhaps for the escaping for non-ASCII Unicode in IRIs.  I think
> > that RDF/XML takes a different and inconsistent stance on this, sometimes
> > allowing the escaping of certain ASCII characters when they appear in
> > RDF/XML.
> > 
> > To illustrate this point
> > 
> > 	http://www.w3.org/foo{bar}
> > 
> > is not a legal URI (or IRI).  However, it is a legal RDF URI reference,
> > because it is a Unicode string that turns into a legal absolute URI with
> > optional fragment identifier when subject to the encoding in Section 6.4 of
> > RDF Concepts.
> I think the above changes mean that all URIs in RDF/XML will either
> pass through the URI Reference Event - and are thus required to be RDF
> URI references - or are hard coded RDF URI references such as
> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
> Can you give an RDF/XML example that demonstrates otherwise?

No, but this is not the point of this problem that I perceive.  (I note that
RDF/XML is indeed syntactically compatible with XML Schema anyURI and XLINK
locator attribute.  (Which, as I read them, are not particularly compatible
with RFC 2396.)  However, RDF uses URI references as tokens and thus needs
to determine identity between them, which puts a higher burden on RDF than
those carried by XML Schema and XLINK.)

The problem can be illustrated with the following very simple question:

Do the following two documents rdf-entail each other?

Document 1:

<rdf:Property rdf:about="http://www.w3.org/foo{bar}" />

Document 2:

<rdf:Property rdf:about="http://www.w3.org/foo%7Bbar%7D" />

If not, why should they not?  It appears to me that they should entail each
other, because the two strings encode the same URI reference.  Are these
two document fragments even valid RDF?  If not, why not?

(The intent is that the %-escapes in Document 2 encode { and }.  If I have
the encoding incorrect, please make the appropriate changes.)

By the way, my understanding of the RDF specifications are that both
documents are indeed legal RDF/XML documents, but that they do not entail
each other because according to Section 6.4 of RDF Concepts
http://www.w3.org/foo{bar} and http://www.w3.org/foo%7Bbar%7D are
different RDF URI references.

Peter F. Patel-Schneider
Bell Labs Research
Received on Thursday, 6 November 2003 14:46:26 UTC

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