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Re: [RDFa] ISSUE-3 @class and @role for rdf:type

From: Mark Birbeck <mark.birbeck@x-port.net>
Date: Thu, 5 Jul 2007 15:14:03 +0100
Message-ID: <640dd5060707050714k3ae7df81h2714c189cf644db8@mail.gmail.com>
To: "Ivan Herman" <ivan@w3.org>
Cc: "Steven Pemberton" <steven.pemberton@cwi.nl>, "Ben Adida" <ben@adida.net>, public-rdf-in-xhtml-tf@w3.org

Hi Ivan,

Thanks for your comments here. This is the first time the @role ==
rdf:type issue has been discussed at the level of RDF, and I've felt
very uneasy that it hasn't been gone through in detail before being
dismissed.


On 05/07/07, Ivan Herman <ivan@w3.org> wrote:
> Well... if you two guys still disagree after all these years, that may
> be one more argument _against_ using @role (not necessarily _for_
> @class, another attribute might also do...):-)

:)


> > In RDF, if you say something is of type 'x' then all sorts of other
> > statements become legitimate. So if I firstly say that 'a toolbar' has
> > a property of 'collection of buttons', and then I subsequently say
> > that 'the second <div> in my document is a toolbar', then it is
> > legitimate to act as if the second <div> in my document has a property
> > of 'collection of buttons'.
> >
>
> Mark, for the records, I am not sure this is true. To formalize it in
> RDF what you seem to say is that if:
>
> [[[
> toolbar a rdfs:Class.
>
> collectionOfButtons a rdfs:Property;
>     rdfs:domain toolbar.
>
> 2ndDiv a toolbar.
> ]]]
>
> then we can deduce that... what? Only that
>
>    2ndDiv collectionOfButtons "something".
>
> is consistent with these, but we _cannot_ deduce that such a triple
> exists somewhere.

Right. But I'm not saying such a triple exists, only that it would be
legitimate to create such a triple--i.e., to use inference.


> You can do what you describe with OWL cardinality constraints describing
> things on collectionOfButtons...
>
>
>
> Actually, we can do something different with those. If the facts are that
>
> [[[
> toolbar a rdfs:Class.
> collectionOfButtons a rdfs:Property;
>     rdfs:domain toolbar.
> 2ndDiv collectionOfButtons "something".
> ]]]
>
> then even in RDFS we can deduce that
>
> [[[
> 2ndDiv a toolbar.
> ]]]
>
> which is somewhat different from what you said.

That's also true, but where did you get the collectionOfButtons
property from for 2ndDiv? It's not in the original mark-up, and it
could only get created (in the sense of being infered) if we were to
say that @role == rdf:type. So we wouldn't be _deducing_:

  2ndDiv a toolbar .

since we already know said it was, because of @role. (Hypothetically.)


> The second example shows that, indeed, rdf typing may have consequences
> (for example if OWL is used), ie, your core argument holds, just the
> example does not:-)

:) I think my example is ok, but I don't really mind. As you say, from
many directions we can see that setting @role to mean rdf:type could
cause problems. My secondary argument is that doing this doesn't
actually gain us anything, and some system is still free to infer from
this:

  2ndDiv role toolbar.

the rdf:type equivalent if it wants to:

  2ndDiv a toolbar.

Regards,

Mark

-- 
  Mark Birbeck, formsPlayer

  mark.birbeck@x-port.net | +44 (0) 20 7689 9232
  http://www.formsPlayer.com | http://internet-apps.blogspot.com

  standards. innovation.
Received on Thursday, 5 July 2007 14:14:10 GMT

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