W3C home > Mailing lists > Public > public-sw-meaning@w3.org > March 2004

Re: Media types for the Semantic Web

From: Mark Baker <distobj@acm.org>
Date: Wed, 31 Mar 2004 13:30:26 -0500
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
Cc: public-sw-meaning@w3.org
Message-ID: <20040331183026.GT11976@markbaker.ca>

On Wed, Mar 31, 2004 at 12:34:35PM -0500, Peter F. Patel-Schneider wrote:
> > 1.  I'm communicating just this graph
> > 2.  I'm communicating this graph and some axiomatic triples
> > 3.  I'm communicating this graph and every inferred triple
> > 4.  I'm communicating this graph, these axiomatic triples, and all
> > inferred triples from the resulting merged graph
> 
> I don't think that *any* of these are appropriate.  What is being
> communicated should be information, not syntax.  (Sometimes the information
> is carried by the particular syntax, but, again, it is the information, not
> the syntax that is being communicated.)

Yes, that's what I mean when I say "communicate a graph".  Sorry if
that's inconsistent with your vocabulary.

> > I believe that using application/rdf+xml handles #1 easily, and #2
> > when the axiomatic triples are the RDF axiomatic triples (since those
> > are equivalent in that case, it seems).  When the axiomatic triples are
> > not (just) RDF's, then a new media type seems necessary.  
> 
> I do agree that attaching different meanings to the syntax should require
> some sort of difference in the communication, be it either a different
> media type or some information carried in the headers, or even a magic
> number at the beginning of the contents (as in Unix).

Great.  I think I've made my position clear that I think the media
type is (currently) the right place for this information.  But I'm
flexible.

> > FWIW, what I
> > believe this suggests is that axiomatic triples should be avoided where
> > possible, precisely because they lead to an explosion of media types
> > (or an explosion of non-self-descriptive messages if new media types
> > aren't minted 8-).  
> 
> Why should there not be many different kinds of meaning associated with
> communications?  There are lots of different kinds of meaning associated
> with human communications, for example.  (Think chat (English) vs chat
> (French).) 

See below...

> > This seemed to be Dan's concern;
> > 
> > ""
> > Now further up the spectrum, we might consider application/owl+xml.
> > 
> > I find that objectionable because it suggests that
> > dublin core and adobe XMP and RSS and so on
> > need their own media types, and it leaves me
> > wondering what media type to use if for
> > a document that mixes all these vocabularies
> > together.
> > ""
> >   -- http://lists.w3.org/Archives/Public/www-webont-wg/2002Oct/0162.html
> 
> Well, what is wrong with this?  Well maybe it is an indictment of using
> media types instead of some other mechanism, but why otherwise?

Deploying new media types is currently expensive; if you have the option
between communicating some information using application/rdf+xml,
instead of with application/prs.pps.foobar+rdf+xml, you should, in
general, opt for the former (unless you know the recipient can handle
it, of course, but obtaining that information doesn't scale).

I can forsee the day when we have dereferenceable media types so that an
agent can, upon seeing an unrecognized one, dereference it to learn that
it's just a specialization of some type it already knows (e.g. in terms
of application/rdf+xml) with its own axiomatic triples.  But until
that's common practice, I think it's best to avoid minting new ones.

Mark.
-- 
Mark Baker.   Ottawa, Ontario, CANADA.        http://www.markbaker.ca
Received on Wednesday, 31 March 2004 13:27:16 GMT

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