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Re: added more examples to RDF/A examples (N3 {} explained)

From: Dan Connolly <connolly@w3.org>
Date: Tue, 18 Oct 2005 15:52:53 -0500
To: Ben Adida <ben@MIT.EDU>
Cc: public-rdf-in-xhtml task force <public-rdf-in-xhtml-tf@w3.org>
Message-Id: <1129668773.25220.21.camel@dirk>

On Tue, 2005-10-18 at 16:35 -0400, Ben Adida wrote:
[...]
> > Under reification, I see
> >
> >  { <> cc:license <http://creativecommons.org/licenses/by-nc-nd/2.5/> }
> > dc:Date "2005-10-18" .

> For my own education, what does the former mean?

It's the subject of ongoing research, actually. The difference has
to do with quoting and use/mention issues. I think this example will
clarify:

If you feed this to cwm*:

:lois :believes [
  rdf:subject :clark;
  rdf:predicate rdf:type;
  rdf:object :Wimp ].
:clark = :superman.
{ ?O1 = ?O2. ?S ?P ?O1 } => { ?S ?P ?O2 }.

and ask it to --think, then it will conclude
that lois thinks that superman is a wimp too:

:lois :believes [
  rdf:subject :clark, :superman;
  rdf:predicate rdf:type;
  rdf:object :Wimp ].

but if you feed this to cwm:

:lois :believes { :clark rdf:type :Wimp }.
:clark = :superman.
{ ?S1 = ?S2. ?S1 ?P ?O } => { ?S2 ?P ?O }.

and ask it to think, it won't find any new conclusions.
The occurrence of :clark within { :clark rdf:type :Wimp }
is quoted.


* I left some prefixes implicit. I think Ben knows what cwm is,
but in case this is anybody's
1st exposure to cwm and N3, see
 Semantic Web Tutorial Using N3
 http://www.w3.org/2000/10/swap/doc/

As to the particular meaning of {} when reduced to an
RDF graph in particular, in the cwm changelog under the 0.8 release
of July 2004:

"See reify/detailed.tests The options, as always, are --reify and
--dereify. The tests for this are now in. There is insufficient
documentation for this feature, and it has not been completely tested,
so there may yet be bugs in it."
 -- http://www.w3.org/2000/10/swap/doc/changes.html#rel0.8

-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
D3C2 887B 0F92 6005 C541  0875 0F91 96DE 6E52 C29E
Received on Tuesday, 18 October 2005 20:53:00 GMT

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