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Re: Media types and assertions

From: Pat Hayes <phayes@ihmc.us>
Date: Thu, 11 Mar 2004 15:04:42 -0600
Message-Id: <p06001f06bc767f7272ae@[]>
To: Mark Baker <distobj@acm.org>
Cc: www-rdf-comments@w3.org

>Hi Pat,
>On Thu, Mar 11, 2004 at 11:07:11AM -0600, Pat Hayes wrote:
>>  The resignation you speak of is real, and represents a kind of blurry
>>  emerging early social consensus that deployed RDF is usually being
>>  used to assert things, mostly.
>Ok, thanks.
>>  Right now, we can muddle along without
>>  needing to 'solve' this problem, which I think is the best thing to
>>  do until the issues become clearer and we all get more experience
>>  with deployed RDF/OWL applications.
>I'm not so sure.  I'm not certain there'll be problems
>>  >I think this is pretty important, and more important than getting the
>>  >registration out (since people are using it, and I haven't observed any
>>  >interop problems with it
>>  Just wait. There will be.
>Perhaps.  But I expect that would only be a result of the ambiguity I
>believe to currently be in the draft.  Which brings us to ...
>>  >).  Ambiguity in media types is not a nice
>>  >thing.
>>  There is no ambiguity.  The media type identifies the XML as being
>>  RDF, which determines how it is to be semantically interpreted and
>>  enables engines to handle it appropriately (parse it, draw valid
>>  conclusions from it, check it for consistency, etc. - all determined
>>  by the specs as they stand). This seems entirely appropriate for a
>>  media type: its like identifying HTML as being HTML. The content of
>>  some RDF - the proposition it expresses - is the same whether it is
>>  being asserted or not, and it is this content that the semantics in
>>  the spec determines.
>>  Media type hasnt got anything to do with social contracts between
>>  sender and receiver. I can use HTML as wallpaper, and it is still
>>  HTML; similarly with RDF.  Whether it is being asserted or denied or
>>  quoted or whatever is another set of issues altogether, which has
>>  more to do with how people behave than with what RDF means.
>Sorry, but I disagree quite strongly.
>If somebody on the Web can't distinguish between an RDF message which
>says "Mark hates bananas" versus one that says "Mark hates bananas (but
>not really)" (aka unasserted),

But that isn't the right way to express the distinction. "Mark hates 
bananas" means what it means in either case, and its this bare 
propositional meaning that the specs talk about and which is 
identified by the media type (I actually think that media type isn't 
the right tool even for this, but I know I'm in a minority on this 
issue and so don't press the point). Not asserting something isn't 
asserting it with a qualification: it is just, well, not asserting it.

You may be assuming that the RDF specs say more than they ever 
intended to say. RDF (and OWL, etc) are only assertional languages 
for describing things. They aren't a kind of universal Web-dialog 
system. Maybe the Web needs such a thing, but if it does then I'd 
like to see it designed with a bit more careful discussion than just 
by inventing a few new media types.

>then there is a failure to communicate.

Communicate about what? The content is communicated accurately. The 
intent of the publisher is not communicated: but where is that 
communicated anywhere on the Web?  Publishers of commercial websites, 
Blogs and webcams may all have very different intentions and goals, 
but they all publish HTML, which is all that the web protocols 
concern themselves with.

Pat Hayes

>The "but not really" part must be part of the message.  It can either be
>done through mechanisms in the RDF specs themselves (e.g.
>parseType="literal"), or it can be done in an encapsulating spec or
>registry, such as the media type registration.
>Mark Baker.   Ottawa, Ontario, CANADA.        http://www.markbaker.ca

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Received on Thursday, 11 March 2004 16:04:45 UTC

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