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RE: encoding of URI references in RDF/XML

From: Jeremy Carroll <jjc@hplb.hpl.hp.com>
Date: Fri, 7 Nov 2003 13:50:03 +0100
To: "Dave Beckett" <dave.beckett@bristol.ac.uk>, "Jeremy Carroll" <jjc@hplb.hpl.hp.com>, <pfps@research.bell-labs.com>
Cc: <www-rdf-comments@w3.org>
Message-ID: <BHEGLCKMOHGLGNOKPGHDKEEHCCAA.jjc@hpl.hp.com>


Hi Peter,

we are treating this comment as a comment on RDF Concepts, particularly:

section 6.4 RDF URI References
http://www.w3.org/TR/2003/WD-rdf-concepts-20031010/#section-Graph-URIref

> 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.

Your understanding was the intent of the documents. Hence there does not
seem to be an issue here.

There is of course the related tag issue

http://www.w3.org/2001/tag/issues.html#URIEquivalence-15

which was resolved with the following draft

http://www.textuality.com/tag/uri-comp-4

the key text being in
http://www.textuality.com/tag/uri-comp-4#ladder

RDF follows XML Namespaces in using "Simple String Comparison" whereas the
alternative in which the two are treated the same is covered in the TAG
finding under "%-Escaping Issues", where I draw your attention to the
observation that due to the potentially unknown character encoding of the
%-escape there is a "(slim) chance of a false-positive in finding these
equivalent"

Thus, the text seems to have been sufficiently clear for you to have
understood the intent, and seems to be in accord with the TAG finding (at
least not at odds with it).

I note that a significant part of the TAG finding is the last section "Good
Practice When Generating URIs".
[[
Those who generate URIs and transmit them, or include them in resource
representations, can make a major contribution to this common good by
understanding the rules in RFC2396 and generating URIs in an at-least-partly
canonicalized form.
]]


Does this adequately address this comment? Or do we need to go further?


thanks

Jeremy

> Date: Thu, 06 Nov 2003 14:46:10 -0500 (EST)
> From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
> To: dave.beckett@bristol.ac.uk
> Cc: www-rdf-comments@w3.org
> Subject: encoding of URI references in RDF/XML (was Re: character encoding
>     in          RDF (including some new related issues))
>
>
> > > 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 Friday, 7 November 2003 07:52:50 GMT

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