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RE: Resolving references against base URIs

From: Al Gilman <asgilman@iamdigex.net>
Date: Tue, 16 Apr 2002 08:23:24 -0400
Message-Id: <200204161223.IAA1640861@smtp1.mail.iamworld.net>
To: Brian McBride <bwm@hplb.hpl.hp.com>, Paul Grosso <pgrosso@arbortext.com>, "Jeremy Carroll" <jjc@hplb.hpl.hp.com>, "Williams, Stuart" <skw@hplb.hpl.hp.com>
Cc: <www-xml-linking-comments@w3.org>, <uri@w3.org>
At 01:15 PM 2002-04-15 , Brian McBride wrote:
>What I have tried to do here is to position RDF as an application built on 
>top of XML and to suggest that XML should not be allowed to express 
>constraints on how applications process it.
>
>There is a deal of sophistry in this argument :( but RFC 2396 doesn't 
>really meet our needs.  Are there any plans to update/refine it in the near 
>future?

Yes, this is a matter on which it would be good to get the TAG to take a position.  But rushing in where angels fear to tread:

The sophistry is too much.

It's not a matter of XML at all.  It's a matter of the semantics of references by URI.  Which is core Web architecture in any document type.

Browsers process same-document references in a special way as directed by RFC-2396.

What you are proposing RDF processors do is to process same-document references in a special way in contradiction to the dictates of RFC-2396.

The RDF model by requiring all URI-references to be absolute makes a same-document reference in accordance with the semantics set forth in RFC-2396 illegal in an RDF document.  Stick to that.

RFC-2396 does provide what you need, just not in a newbie friendly syntax.  You can force BASE-ifying of referenced items simply by not using fragment-only syntax in the reference.

For consideration in future revisions:

Just as Larry has suggested that in MIME transport we need a reserved floating pseudo-prefix of "this document" which I would compare with the classical academic 'ibid.,'  what you are finding would be newbie-friendly in RDF would be a reserved floating pseudo-prefix of "per base in context" or 'loc. cit.'

Al

>At 09:51 15/04/2002 -0500, Paul Grosso wrote:
>>At this point, it looks like we are all using different phrases
>>(not even sentences) in various specs to support different views.
>>
>>My view is that an RDF resource should be something of MIME type XML,
>>and anything of MIME type XML that does anything with XML Base has to
>>interpret things the same way.  I would consider this an architectural
>>issue, so maybe it's time this issue should be sent to the TAG.  (Two
>>of the three authors of RFC 2396 are on the TAG.)
>
>Hi Paul,
>
>It may be that this needs to go the tag, but I'd like to make sure we do 
>our best to clarify the issue first.  I hope Jeremy will forgive me butting in.
>
>I'll try to keep this short, but it may be a little long.
>
>First: the problem RDF is trying to solve.  The current RDF specs have 
>encouraged the use of the following idiom:
>
>   <rdf:Description rdf:about="#foo">
>     ...
>
>The value of the rdf:about attribute is turned into an absolute URI 
>reference by concatenating the '#foo' with the URI of the containing document.
>
>This causes problems.  Folks copy the file from the web to their hard drive 
>so they can work on it in a plane, and the uri changes to something like 
>file:c:\temp\....rdf and this is really useless for rdf users.  Or folks 
>wish to include RDF in say a message protocol where  there is no base uri 
>of the document.
>This is the cause of one of, if not the, most frequent newbie problem with 
>DAML that we see on jena-dev.

>
>So we are looking for a way to retain this convenient syntax, but have the 
>uri's produced not change when the file is copied or mirrored.
>
>To appreciate what is happening here, we need to look at a semi-fictional 
>RDF processing pipeline:
>
>
>input xml document -> xml parser -> rfc2396 processor -> rdf parser -> rdf 
>graph
>
>We start with an xml document and end up with a datastructure.  The 
>datastructure is not a DOM; its not a representation of an xml 
>document.  It is as far as xml is concerned, an application data structure.
>
>For each value of an rdf:about attribute, the rfc2396 processor outputs 
>either an absolute URI or a same document reference.  The absolute URI is 
>processed according to RFC2396.  Same document references are recognised 
>according to RFC 2396.
>
>All is in conformance with rfc 2396 at this point.
>
>Now the RDF parser comes in to play and it is required to transform the 
>value of each rdf:about attribute into an absolute uri reference.  If the 
>RFC 2396 processor has produced an absolute uri reference, it need do 
>nothing.  If however, it is a same document reference, then, just as a 
>browser will handle same document references specially, so does RDF.  It 
>transforms the same document reference into an absolute URI according to an 
>algorithm defined by the RDF specs.  The mimetype of an rdf document will 
>be text/xml+rdf.  As far as xml base and rfc 2396 are concerned, this is 
>application code over which they have no say.
>
>What I have tried to do here is to position RDF as an application built on 
>top of XML and to suggest that XML should not be allowed to express 
>constraints on how applications process it.
>
>There is a deal of sophistry in this argument :( but RFC 2396 doesn't 
>really meet our needs.  Are there any plans to update/refine it in the near 
>future?
>
>Brian
> 
Received on Tuesday, 16 April 2002 08:28:27 GMT

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