W3C home > Mailing lists > Public > www-rdf-interest@w3.org > December 2002

Re: Having it Both Ways (and Ending URI Confusion)

From: Sandro Hawke <sandro@w3.org>
Date: Fri, 13 Dec 2002 16:59:01 -0500
Message-Id: <200212132159.gBDLx1T28400@wadimousa.hawke.org>
To: www-rdf-interest@w3.org

> Of course rdf:about is considered a bit of syntax, not a property.
> The first two examples each generate one triple, while the second two
> each generate two triples.  I think that's the price we pay for adding
> the extra bit saying which technique we're using for identifcation and
> grounding via the web.
> If the RDF Core WG could pick one of the properties (ns:URI or
> ns:homePageURI) as the "true" meaning of rdf:about, then either 3 or 4
> would drop back down to one triple.  But I'm afraid either option
> leaves a lot of existing RDF out in the cold.  So perhaps we're best
> off recognizing that rdf:about is ambiguous and best avoided in favor
> of these two new predicates.

I should revise this a bit and explain more.  Just avoiding rdf:about
doesn't solve the problem (and let the WG ignore it), because we still
have rdf:resource and the elements of the rdf and rdfs namespace to
worry about.

Does "http://www.w3.org/1999/02/22-rdf-syntax-ns#type" denote a web
page fragment or an RDF property?  (In MT terms, does that label on a
node mean the the node is a web page or a Property?)  RDF says it's a
property, but claiming the URI itself directly denotes the property is
just... so.... contorted in terms of existing specification,
understandings, and deployed systems.  The "escape hatch" that the
content will be served with media type "application/rdf+xml" (and so
it can have whatever semantics RDF Core WG wants) seems to me like a
complete hack, since since rdf+xml is still XML [1], and XML already
has deployed XPointer fragment semantics [2].

So the answer is really simple.  RDF just has to recognize that in
most of its use of URIs, the URIs identify things by identifying their
home pages or home page fragments.  And when you want to author RDF
which is actually talking about web pages, you can either use a
(possibly-never-published) web page about that web page, or use
another property, which I'd suggest calling rdf:URI or rdfs:URI.

Existing RDF code should be re-examined to see which kind of relation
is intended.  I suspect 99% of the time, non-URI-Ref URIs are being
used to denote the resource itself (and so should be converted to use
rdf:URI), with URI-Ref URIs being okay as is.

The canonical example 

  <rdf:Description about="http://www.w3.org/Home/Lassila">
    <s:Creator>Ora Lassila</s:Creator>

should then be

  <rdf:Description rdf:uri="http://www.w3.org/Home/Lassila">
    <s:Creator>Ora Lassila</s:Creator>

I suppose I should review all the RDF Core WG documents and see just
what would need to be changed to make this happen.   Ugh...

    -- sandro

[1] http://www.ietf.org/rfc/rfc3023.txt
[2] http://www.w3.org/TR/xptr-framework/#shorthand
    [ Note that I'm using a URI-Ref there to refer to a section 
      of a document.  That does seemt to be standard usage, 
      doesn't it? ]
Received on Friday, 13 December 2002 17:00:10 UTC

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