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

From: Jeremy Carroll <jjc@hplb.hpl.hp.com>
Date: Fri, 8 Mar 2002 09:44:09 -0000
To: "Graham Klyne" <GK@NineByNine.org>, "RDF core WG" <w3c-rdfcore-wg@w3.org>
Message-ID: <JAEBJCLMIFLKLOJGMELDOEEACDAA.jjc@hplb.hpl.hp.com>

I concur with Aaron's comments:

> I remember three bullet
> points: [..], putting a "here be dragons"
> warning in the appropriate spec [...]

Graham's text did not IMO meet that part.
I am not sure whether dragons get into the primer.
If so, how about:

> <<<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.
> 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
<em>is</em> dependent upon the representation accessed by the  URL alone.
in RDF, the thing identified by a URI with fragment identifier <em>does
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.
> 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.

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.
> <<<FINISH>>>
> ------------
> Graham Klyne
Received on Friday, 8 March 2002 04:45:38 UTC

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