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RE: 2002-02-25#19, Fragment identifiers, words for the primer

From: Graham Klyne <GK@NineByNine.org>
Date: Fri, 08 Mar 2002 11:11:33 +0000
Message-Id: <5.1.0.14.2.20020308110501.03f928e0@joy.songbird.com>
To: "Jeremy Carroll" <jjc@hplb.hpl.hp.com>
Cc: "RDF core WG" <w3c-rdfcore-wg@w3.org>
At 09:44 AM 3/8/02 +0000, Jeremy Carroll wrote:
> > <<<START>>>
> >
> > Fragment identifiers, when used with RDF, are treated as a simple
> > extension
> > of the URI to which they apply, whose interpretation is not dependent on
> > the context in which they appear.  This reflects the fact that
> > there is no
> > special treatment of the fragment identifier part of URIrefs in the model
> > theory for RDF -- that is, they are simply a syntactic part of a
> > name that
> > denotes some resource.
> >
>[[[ DELETE:
> > There is sometimes an unwarranted expectation that the thing
> > identified by
> > a URI with fragment identifier bears some particular relationship to the
> > thing identified by the URI alone.
>]]]
>[[[ ADD:
>In standard usage, the representation accessed by a  URL with a fragment
>identifier
><em>is</em> dependent upon the representation accessed by the URL alone.
>However,
>in RDF, the thing identified by a URI with fragment identifier <em>does
>not</em>
>bear any particular relationship to the thing identified by the URI alone.
>]]]

OK, I can see this is generally an improvement, but I'd want to change the 
opening clause to:

"In standard usage for web document retrieval, ...".  I might also suggest 
changing "dependent upon" to "related to".

Also, to fully discharge my action w.r.t. MIME types, here's a proposed new 
version:

[[[
In standard usage for web document retrieval, the representation accessed 
by a URL with a fragment
identifier is related to the representation accessed by the URL alone, in a 
way that depends on the MIME type of the document representation 
retrieved.  However, in RDF, the thing identified by a URI with fragment 
identifier does not bear any particular relationship to the thing 
identified by the URI alone.
]]]


> > For example, the RDF statement:
> >
> >     urn:isbn:0-520-02356-0#page10 ex:contains "metatheory" .
> >
> > might be regarded as having a particular relationship to the statement:
> >
> >     urn:isbn:0-520-02356-0 dc:title "Metalogic" .
> >
> > but this would be an error.  As far as RDF is concerned,
> > 'urn:isbn:0-520-02356-0#page10' and 'urn:isbn:0-520-02356-0' are two
> > different names with no defined relationship.  This is different from the
> > normal use of fragment identifiers when retrieving web documents,
> > where the
> > URI with fragment identifier is taken to represent some view of the
> > document referenced by the URI alone.
> >
> > This is not to say that a URI and that URI with fragment identifier may
> > never be related, just that no such relationship is presumed by
> > RDF.  Returning to the example above, it is quite possible that some RDF
> > document defines a relationship between these terms:
> >
> >      urn:isbn:0-520-02356-0 rdf:type ex:Book .
> >      urn:isbn:0-520-02356-0 dc:title "Metalogic" .
> >       :
> >      urn:isbn:0-520-02356-0 ex:consistsOf _:a .
> >        _:a rdf:type rdf:Seq .
> >        _:a rdf:_1 urn:isbn:0-520-02356-0#page1 .
> >        _:a rdf:_2 urn:isbn:0-520-02356-0#page2 .
> >         :
> >        _:a rdf:_10 urn:isbn:0-520-02356-0#page10 .
> >         :
> >        (etc.)
> >
> > This RDF graph makes specific assertions about relationships
> > between things
> > denoted by the URI and URI-with-fragment-identifier.
> >
>[[[ DELETE:
> > Finally,
>]]]
> > [N]ote that in the special case of a document containing RDF/XML
> > statements (MIME type application/RDF+XML???), the syntax presumes a
> > convention for relating the document name to the resource names whose
> > definitions it contains.  Specifically, resources described using an
> > rdf:ID='...' attribute have an identifier that consists of the
> > RDF document
> > URI plus a fragment identifier of the given rdf:ID attribute value.  But
> > observe that this is a purely syntactic convention, and does not
> > of itself
> > presume any semantic relationship between the defining document and the
> > thing defined.
>
>[[[ADD:
>Finally, other non-RDF components of a system may expect to be
>able to treat a URI with fragment identifier in a manner similar to
>the treatment of a URL with fragment identifier used for document
>retrieval over the web. This may lead to interoperability problems.
>]]]

I think that if this is to be included, we need some justification (e.g. an 
example where interoperability fails).  I have found it hard to come up 
with a convincing case.  From my exchanges with Pat, I think the dragons 
may not be as fiery as we first thought if we are clear about the 
accidental nature of any relationship between URI and URI#frag as far as 
RDF is concerned.

> > <<<FINISH>>>
>

------------
Graham Klyne
(GK@ACM.ORG)
Received on Friday, 8 March 2002 08:40:03 EST

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