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Re: POWDER: my rabbit

From: Phil Archer <parcher@icra.org>
Date: Mon, 17 Dec 2007 16:28:02 +0000
Message-ID: <4766A392.6050305@icra.org>
To: Jeremy Carroll <jjc@hpl.hp.com>
CC: www-archive@w3.org, "Carroll, Jeremy John" <jeremy.carroll@hp.com>, Dan Brickley <danbri@danbri.org>, "Williams, Stuart (HP Labs, Bristol)" <skw@hp.com>, Ivan Herman <ivan@w3.org>, Bijan Parsia <bparsia@cs.man.ac.uk>

That sounds very much in line with some of our discussions.

For example, we have discussed using a GRDDL transform to go from a 
simple XML doc to something more complex that has the RDF constructs in 
it (Fabien Gandon was with us at TPAC). This also fits in with a 
conversation I had with David Booth where, again, we talked about simple 
thing -> GRDDL -> complex thing but where the semantics were always 
defined in terms of the complex 'full model'.

We're mindful of the need to make sure that whatever is published as a 
DR is not going to be misinterpreted by an off the shelf OWL/RDF tool. 
Achieving that whilst benefiting from the expressivity of SW 
technologies does seem to be pointing towards a multi-layered approach.

Phil.


Jeremy Carroll wrote:
> Attempting to pull something from my hat ....
> 
> How about:
> 
> a)
> 
> - a POWDER document has a root element, typically wdr:DR, in the POWDER 
> namespace.
> 
> - a POWDER document is an RDF/XML document
> 
> - an RDF/XML document that uses POWDER vocabulary but does not have a 
> root element in the POWDER namespace is not a POWDER document
> 
> b)
> 
> POWDER documents are constrained by some schema (probably not an XML 
> Schema) so that they roughly follow the pattern given at
> 
> http://www.w3.org/TR/2007/WD-powder-dr-20070925/#structure
> 
> or some other similar pattern
> 
> c)
> 
> A POWDER processor follows an operational semantics, roughly following 
> the instructions of the various published WDs
> 
> d)
> 
> As an RDF/XML document, the formal semantics of a POWDER document is 
> arranged to be true, but weaker than the operational semantics.
> 
> e)
> A GRDDL transform is associated with the POWDER namespace
> 
> f)
> The GRDDL transform transforms
> 
> 7      <wdr:ResourceSet>
> 8        <wdr:includeHosts>example.org</wdr:includeHosts>
> 9      </wdr:ResourceSet>
> 
> into
> 
> 1  <owl:Class>
> 2
> 3    <owl:equivalentClass>
> 4      <owl:Restriction>
> 5        <owl:onProperty rdf:resource="&powder;#includeHost" />
> 6        <owl:hasValue>example.org</owl:hasValue>
> 7      </owl:Restriction>
> 8    </owl:equivalentClass>
> 9  </owl:Class>
> 
> 
> etc. (i.e. the GRDDL transform embeds expert knowledge of OWL).
> 
> g)
> The formal semantics of the GRDDL result of a POWDER document 
> corresponds closely to the operational semantics of the POWDER document.
> 
> h)
> The formal semantics of a POWDER document read by a non-GRDDL aware, 
> non-POWDER aware, RDF processor is a proper consequence of the formal 
> semantics of a POWDER aware and GRDDL aware reading of the same document.
> 
> ====
> 
> That seems to hit enough of the targets.
> 
> Some obvious drawbacks
> 
> It continues an overly technocractic semantic web
> where there is a two-tier (or even three tier) system of formalism, with 
> the 'true' definitions being defined on the 'highest' plane, that is 
> accessibly only to an elite with a particular type of 
> mathematical/logical background.
> 
> There continues to be a divorce between an operational practice, that is 
> probably defined in terms of POWDER as XML documents, and actually 
> implemented using SAX and DOM like interfaces, and a theoretical model, 
> built on semantic web recommendations.
> 
> ...
> 
> Jeremy
> 
> 

-- 
Phil Archer
Chief Technical Officer,
Family Online Safety Institute
w. http://www.fosi.org/people/philarcher/
Received on Monday, 17 December 2007 16:28:37 GMT

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