W3C home > Mailing lists > Public > public-rdf-in-xhtml-tf@w3.org > December 2005

Re: [ALL] [HTML] reification in rdf/a

From: Mike Linksvayer <ml@creativecommons.org>
Date: Fri, 09 Dec 2005 15:13:08 -0800
To: Dan Brickley <danbri@w3.org>
Cc: Ben Adida <ben@mit.edu>, SWBPD list <public-swbp-wg@w3.org>, public-rdf-in-xhtml-tf@w3.org
Message-Id: <1134169988.8381.73.camel@localhost.localdomain>

Hi, delurking for a second, as this is important for CC and I've always
been personally a bit confused by the notion that reification is
problematic (apart from the usual RDF/XML syntax issues).

The inference below that b was licensed on the same date as a seems
correct.  owl:sameAs says a and b are the same thing.  Of course any
assertion about one is true of the other, though it is silly to say
"other", as we've said they are identical.

I'm not entirely certain upon re-reading
http://www.w3.org/TR/owl-ref/#sameAs-def whether "same" means ==
or .equals() (i.e., identity or equality), which could make a
difference.

But in any case, any ambiguity there is would arise from inappropriate
use of owl:sameAs, not reification.

<http://a.example.org> dc:title "foo" .
<http://b.example.org> dc:title "Foo" .
<http://b.example.org> owl:sameAs <http://a.example.org> .

presumably allows one to infer

<http://a.example.org> dc:title "Foo" .

No reification involved.  Looks analogous to the example below that does
involve reification.  (I don't see a problem in either case, but if
there is a problem, it is in both cases.)

This is important to CC because we'd like people to be able to make
assertions about license assertions (e.g., who, effective date,
warranty), in addition to straightforward assertions about works and
licenses.  The latter are too imprecise when a work is potentially
offered under multiple licenses by multiple rights holders.


On Fri, 2005-12-09 at 17:05 -0500, Dan Brickley wrote:
> * Ben Adida <ben@mit.edu> [2005-12-09 13:03-0500]
> > 
> > Dan,
> > 
> > Thanks for this point, and apologies for my delayed response.
> > 
> > Is it the sense of the Working Group that reification is, itself, not  
> > a Best Practice for RDF?
> > 
> > I ask because your concern seems to be a generic concern about  
> > reification, not one about RDF/A's implementation of it specifically.  
> 
> 
> Yup. It's a general point about the RDF'99 reification vocab
> (rdf:Statement but more specifically the associated properties
> rdf:predicate rdf:subject and rdf:object). The same objection applies
> to any and all RDF notifications, eg. GRDDL.
> 
> I'm interested to find out if others on the WG share my concern, and 
> hope that any recharted WG could offer some written down advice in this
> area.
> 
> Dan
> > So far, we've tried to build as much of RDF as possible into RDF/A,  
> > without prejudice as to which feature we implement, other than the  
> > inherent limitations of trying to express RDF in XHTML with as much  
> > simplicity as possible. To forgo reification for the reason below  
> > would be a slight departure from our approach to date: it would mean  
> > that we think the concept of reification is, itself, not a best  
> > practice and thus not a practice we want to encourage with a compact  
> > RDF/A reification notation.
> > 
> > Thus, I'm wondering if this belief -- that reification is generally  
> > bad news -- is widespread within the working group.
> > 
> > -Ben
> > 
> > On Nov 4, 2005, at 12:53 PM, Dan Brickley wrote:
> > 
> > >
> > >
> > >I have a concern about RDF/A encouraging usage of the old RDF  
> > >Reification vocab, eg. as in
> > >http://www.w3.org/2001/sw/BestPractices/HTML/2005-rdfa- 
> > >primer#id0x0382be98
> > >
> > ><link about="" rel="cc:license"
> > >     href="http://creativecommons.org/licenses/by-nc-nd/2.5/">
> > >  <meta property="dc:date" content="2005-10-18" />
> > ></link>
> > >
> > >yields:
> > >
> > >[ rdf:subject <>;
> > > rdf:predicate cc:license ;
> > > rdf:object <http://creativecommons.org/licenses/by-nc-nd/2.5/> ]
> > >dc:date "2005-10-18" .
> > >
> > >My concern is that this vocab (rdf:subject/predicate/object/etc)  
> > >appears to be a quoting mechanism, but isn't. So it interacts with  
> > >other RDF statements in a way that is likely to cause confusion.
> > >
> > >Imagine in the data above that <> is <http://a.example.org/> (to  
> > >avoid relative URIs confusing things)...
> > >
> > >What inferences go through if we believe that (excuse the notation,  
> > >not sure if this is turtle)
> > >
> > ><http://a.example.org/> owl:sameAs <http://b.example.org/> .
> > ><http://creativecommons.org/licenses/by-nc-nd/2.5/> owl:sameAs  
> > ><http://creativecommons.org:80/licenses/by-nc-nd/2.5/> .
> > >
> > >I think this gets us.....
> > >
> > >[ rdf:subject <http://b.example.org>;
> > > rdf:predicate cc:license ;
> > > rdf:object <http://creativecommons.org:80/licenses/by-nc-nd/2.5/> ]
> > >dc:date "2005-10-18" .
> > >
> > >While in the current example, the "dc:date = 2005-10-18" claim  
> > >might be true, I don't think it follows that all such attempts at  
> > >reification will make sense given the interaction with OWL-powered  
> > >identity reasoning.
> > >
> > >For example,
> > >
> > >
> > ><link about="http://z.example.com/" rel="cc:license"
> > >     href="http://creativecommons.org/licenses/by-nc-nd/2.5/">
> > >  <meta property="xyz:reviewerNotes" content="Dan reviewed this." />
> > ></link>
> > >...if there are a number of other things that are owl:sameAs http:// 
> > >z.example.com/  .... for which the reification statements might be  
> > >inappropriate, depending on the semantics of the meta property.
> > >
> > >Hope these hurried notes make sense,
> > >
> > >Dan
> > >
> > >
> 
-- 
  Mike Linksvayer
  http://creativecommons.org/about/people#21
Received on Friday, 9 December 2005 23:15:20 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Tuesday, 8 January 2008 14:15:00 GMT