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Re: Namespaces wihtout "#" Was: Few CWM Bugs

From: Graham Klyne <GK@ninebynine.org>
Date: Mon, 26 Nov 2001 16:59:11 +0000
Message-Id: <5.1.0.14.2.20011126164115.032bb490@joy.songbird.com>
To: "Tim Berners-Lee" <timbl@w3.org>
Cc: <www-rdf-interest@w3.org>
At 10:39 AM 11/26/01 -0500, Tim Berners-Lee wrote:
>Fortunately, the fragment ID allows us to refer to something defined
>or described by the document, and that can be quite abstract.

Hmmm... this feels like an uncomfortable overloading of fragment identifier.

Before responding to this, I checked out your 
http://www.w3.org/DesignIssues/Fragment.html (which, BTW, has been updated 
recently but there's no record of the update)...


[Remaining quotes are from: http://www.w3.org/DesignIssues/Fragment.html]

>The fragment identifier is a string at the end of a URI which identifies,
>within a Web document, a part or view to which one refers.

[...]

>Axiom
>The significance of the fragment identifier is a function of
>the MIME type of the object

>Fragment identifiers for RDF identify concepts
>The semantic web has information about anything. The fragment identifier on
>an RDF (or N3) document identifies not a part of the document, but whatever
>thing, abstract or concrete, animate or innanimate, the document describes as
>having that identifier.

I have a couple of problems with this:
(a) this is rather at odds with the earlier definition of identifying 
something "within a web document".

(b) It's not clear to me that RDF is unequivocally associated with a MIME 
type.   What's the MIME type of RDF embedded in an XHTML document?

>It is important, on the  Semantic Web, to be clear about what is
>identified. An http: URI (without fragment identifier)
>necessarily identifies a generic document. This is
>because the HTTP server response about a URI can deleiver a rendition of (or
>location of, or apologies for) a document which is identified by the URI 
>requested.  A client which understands the http: protocol can immediately
>conclude that the fragementid-less URI is a generic document.  This is true
>even if the publisher (owner of the DNS name) has decided not to run a server.
>Even if it just records the fact that the document is not available online,
>still a client knows it refers to a document.  This means that identifiers for
>arbitrary RDF concepts should have fragment identifiers.  This in term means
>that RDF namespaces should end with "#".

[Aside:  this last bit is new new me;  it's very disconcerting when these 
ideas seem to pop out of the woodwork.]

[...]
>User awareness of the form of a reference
>Clearly when a fragment ID is generated and associated with a URI which is
>generic in any way (language, version, etc as well as content-type), then
>there is a possible failure of the fragment-id refers to something which is
>not defined in any specific instance.  It would be appropriate for a client,
>when generating a link (or bookmark, etc) to provide the user with a choice
>of
>A bookmark to the whole living document, or
>A bookmark to a specific part of a "dead" version;
>Intermediate combinations.
>As both these options are meaningful and useful, they will have to surface
>at the user interface level.

Maybe this last point indicates part of the confusion I feel here:  with 
RDF, I think it's fair to say that that which is referenced does *not* have 
to surface at the UI level -- it's part of an identifier that may be 
exchanged between systems without regard for user presentation or 
containing document.

It seems to me that RDF uses fragment identifiers in a different way than 
web retrieval applications.  Is it really harmful to just say that RDF is 
different in this respect?  I can't help feeling that this attempt to fit 
RDF interpretation into some variant of the web browsing mould will 
generate more confusion than clarity.

#g


------------
Graham Klyne
GK@NineByNine.org
Received on Monday, 26 November 2001 12:12:02 GMT

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