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Re: Media types for the Semantic Web

From: Mark Baker <distobj@acm.org>
Date: Wed, 7 Apr 2004 12:51:30 -0400
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
Cc: public-sw-meaning@w3.org
Message-ID: <20040407165130.GV11976@markbaker.ca>

On Wed, Mar 31, 2004 at 03:25:51PM -0500, Peter F. Patel-Schneider wrote:
> > So by "what if you don't", do you mean that there's no equivalent
> > licensed-as-RDF graph which can communicate that same information?
> 
> Precisely.  There are far more things under the sun than RDF can imagine.
> (I wish I knew the source of this ``quote'' - it doesn't appear to be on
> the web.)

Understood.  I suppose the difference between something like owl:sameAs
and your run-of-the-mill foo:bar predicate is that the former, when
added, changes the existing graph rather than just extending it,
wouldn't you say?  (Aside; is there a name for these sorts of
predicates?).  I'm wondering whether a mandatory extension mechanism
in RDF wouldn't be appropriate when such a predicate was used, in order
to permit the sender to say "If you don't understand this predicate,
then you can't build the graph that I'm trying to communicate"?  That
seems sensible to me.

DanC also said something to me at one point (can't find it), that he
felt there was an argument to be made for assuming that any use of
the OWL namespace (or maybe it was rdfs) necessarily imports OWL (rdfs)
semantics.  While that would certainly be a simple solution, I don't
believe it to be a workable (scalable) one, as given an arbitrary RDF
document, one would not know whether or not some namespace required
such importation, and therefore whether one was able to understand the
meaning of the graph as intended by the sender.  But ... mandatory
extensions might help there, I think, so that a sender could label any
predicate requiring importation as "must understand"; if the recipient
understood the predicate, then it would presumably understand the
intended semantics and could do the right thing.  If it didn't, at
least it would know it was missing out on some triples.

Anyhoo, though I'm currently leaning towards the need for an OWL media
type based on these arguments, I'm not totally convinced one way or the
other, and probably won't be until I've fully absorbed this discussion
and the ideas I just presented above.  I'm sure there'll be opportunies
to pick this topic up again in the future.

P.S. I see that there's a new workshop on compound documents[1] in a
couple of months which is great, though it seems more geared towards
human-targetted formats like XHTML/SVG/etc..  But they're still asking
some of the tough questions, such as;

  - How should a Web application and its related resources (e.g.
    images, sounds) be packaged?
  - What MIME type should a compound document use?

 [1] http://www.w3.org/2004/04/webapps-cdf-ws/index.html

Cheers,

Mark.
-- 
Mark Baker.   Ottawa, Ontario, CANADA.        http://www.markbaker.ca
Received on Wednesday, 7 April 2004 12:52:28 GMT

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