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RE: Heads up: RFC2996bis, possible problem for RDF

From: Graham Klyne <gk@ninebynine.org>
Date: Tue, 17 Feb 2004 15:53:27 +0000
Message-Id: <5.1.0.14.2.20040217154401.02553bf0@127.0.0.1>
To: "Jeremy Carroll" <jjc@hplb.hpl.hp.com>, "rdf core" <w3c-rdfcore-wg@w3.org>

At 15:30 17/02/04 +0100, Jeremy Carroll wrote:
>This does not look disastrous to me.
>
>In RDF URIrefs ending in # (i.e. with explicitly empty fragment) only
>regularly occur as namespace names. All possible uses of such URIrefs
>involve qnames which give them a non-emtpy fragment part.
>
>The text in question
>
>"URI producers and normalizers should omit a delimiter if the component it
>delimits is empty"
>
>uses a "should" not a "MUST", and is hence sufficiently weak.

Yes, but the text also seems to claim that it is always safe to apply the 
normalization.  That is my concern.  Section 6.1 says "...  while strictly 
avoiding false positives".

>We perhaps could suggest modifying the text:
>[[
>
>, with one exception: a double-slash delimiter indicating an authority
>component should not be removed, even when the authority is empty, since
>doing so can lead to misinterpreting the path.
>]]
>http://gbiv.com/protocols/uri/rev-2002/rfc2396bis.html#normalize-empty
>
>to
>[[
>. A first exception is: a double-slash delimiter indicating an authority
>component should not be removed, even when the authority is empty, since
>doing so can lead to misinterpreting the path.
>A second exception is: a common idiom in RDF/XML uses URI references with
>empty fragments as XML namespace names.
>]]

I think it would also apply to empty path and query components, so I'm not 
happy to just pick out empty fragments as a second exception.

>The overall normalization rules in section 6
>http://gbiv.com/protocols/uri/rev-2002/rfc2396bis.html#comparison
>inevitable create a many positive matches that are not honoured in RDF
>concepts. Like XML namespaces we chose the simplest possible definition of
>equality: string equality. The overall tone of section 6 ought to respect
>such a choice.

Yes.  I'm waiting to see what response to my comments, but I think I might 
suggest that the text:
[[
Therefore, comparison methods are designed to minimize false negatives 
while strictly avoiding false positives
]] -- (section 6.1)

be something like
[[
Therefore, comparison methods are designed to minimize false negatives 
while strictly avoiding false positives when used for purposes of retrieval.
]]

(This echoes the earlier comment "URI comparison is performed in respect to 
some particular purpose" [section 6 intro], and I think provides the 
necessary escape route for RDF and XML namespaces and maybe other purposes 
to which URIs are pressed.)

#g
--

> > -----Original Message-----
> > From: w3c-rdfcore-wg-request@w3.org
> > [mailto:w3c-rdfcore-wg-request@w3.org]On Behalf Of Graham Klyne
> > Sent: 17 February 2004 13:17
> > To: rdf core
> > Subject: Heads up: RFC2996bis, possible problem for RDF
> >
> >
> >
> > I've just reviewed:
> >
> >     http://gbiv.com/protocols/uri/rev-2002/rfc2396bis.html
> > Modified: 16 February 2004 11:36:15
> > Size: 167.42 KB (171437 bytes)
> >
> > Which has recently been "last called" in the IETF URI informal group in
> > preparation for an IESG last-call request, per:
> >    http://lists.w3.org/Archives/Public/uri/2004Feb/0082.html
> >
> > I am concerned that the empty component normalization rules may be
> > troublesome for RDF.  My review comments are at:
> >    http://lists.w3.org/Archives/Public/uri/2004Feb/0094.html
> >
> > The specific example raised is:
> >
> > [[[[
> > Section 6.2.2.3:
> > I'm concerned about empty component normalization:
> > In RDF usage, the URIs:
> >      http://example.org/
> > and
> >      http://example.org#
> > would result in quite distinct resource identifiers, e.g. in:
> >
> > [[
> > Triples of the Data Model in N-Triples Format (Sub, Pred, Obj)
> >
> > <http://www.w3.org/RDF/Validator/run/foo>
> > <http://example.org/prop> "value" .
> >
> > The original RDF/XML document
> >
> > 1: <?xml version="1.0"?>
> > 2: <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
> > 3:   xmlns="http://example.org/">
> > 4:   <rdf:Description rdf:about="foo">
> > 5:     <prop>value</prop>
> > 6:   </rdf:Description>
> > 7: </rdf:RDF>
> > ]]
> >
> > and
> >
> > [[
> > Triples of the Data Model in N-Triples Format (Sub, Pred, Obj)
> >
> > <http://www.w3.org/RDF/Validator/run/foo>
> > <http://example.org#prop> "value" .
> >
> > The original RDF/XML document
> >
> > 1: <?xml version="1.0"?>
> > 2: <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
> > 3:   xmlns="http://example.org#">
> > 4:   <rdf:Description rdf:about="foo">
> > 5:     <prop>value</prop>
> > 6:   </rdf:Description>
> > 7: </rdf:RDF>
> > ]]
> >
> > (RDF triples generated by http://www.w3.org/RDF/Validator/)
> >
> > Are distinct RDF graphs, even though the URIs are equivalent under the
> > normalization rules given.
> > ]]]]
> >
> > #g
> >
> >
> > ------------
> > Graham Klyne
> > For email:
> > http://www.ninebynine.org/#Contact
> >
> >

------------
Graham Klyne
For email:
http://www.ninebynine.org/#Contact
Received on Tuesday, 17 February 2004 10:55:07 UTC

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