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Re: POWDER: thoughts

From: Phil Archer <parcher@icra.org>
Date: Fri, 14 Dec 2007 16:59:52 +0000
Message-ID: <4762B688.7070905@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>

Jeremy Carroll wrote:
> Cc-ing ivan and bijan since they seem interested.
> I am going to start a variety of threads on www-archive, with the intent 
> that we pick the threads up on the tuesday meeting.
> I take it that the theme of the discussion is trying to evaluate powder 
> design options to get appropriate balance between 'correctness' with 
> respect to the more mathematical bits of the SW Recs (OWL and RDF), and 
> usability by the intended user base.

That is the essential tension we are trying to resolve, yes.

> The ideal outcome would be one where small amounts of attention to 
> detail, make little to no impact on usability, but enhance 'correctness' 
> and hence interoperability with off-the-shelf SW tools.

Indeed. As you have discerned, Jeremy, usability is a high priority 
since we hope that POWDER will be of use well beyond the traditional 
Semantic Web Community and therefore by some people for whom the 
mathematical exactness of the RDF/OWL model will of little immediate 

> Poor outcomes would be ones in which tension between the two objectives 
> (correctness and usability) become conflict; and either POWDER users 
> feel that usability is sacrificed for ill-defined and elitist logical 
> goals, or the SW specs, at least their logical parts, are simply ignored 
> because they are unhelpful.


> I'll try and start these threads:
> - reification, or what?
>    I dislike reification, and will argue against it, and in favour of 
> the design in the powder-dr WD, with minor mods.

I find this both pleasing and surprising. The POWDER WG has been working 
with the structure in the currently published WD [1] for a good length 
of time and we're comfortable with it as an image in our heads - 
_however_ we do not, of course, want to promote something that is 
clearly 'wrong' in an SW sense. So if we could fix the model with minor 
modifications to [1] - I think we'd be smiling all the way.

> - resource descriptions, as a semantic extension??
>   RDF semantics makes no provision for examining the IRIs used for 
> resources. This is not addressed by OWL 1.0 or OWL 1.1. This is 
> fundamental to POWDER; and should, in my view, be addressed by formally 
> creating a suitable semantic extension.

Sounds good to me.

> - resource descriptions and monotonicity
>   I got a bad non-monotonic feeling while reading the powder-grouping 
> WD; interestingly it was while reading bits that had clearly been 
> written with the issue in mind :(

 From my perspective it seems that the problem that jumps out at SW folk 
in the grouping of resources doc [2] makes them jump to the 
OWL-based/sub class of approach as exemplified in [3] and graphed at [4] 
. But this then introduces reification which makes people run back the 
other way!

Actually, I played with the reification issue a little today - and 
_didn't_ put an ID on the subClassOf triple, i.e. the assertion that A 
is a subclass if B is only in the reification triple - which gives the 
RDF at [5] and the graph at [6] - which I have to say doesn't look too 
bad to my inexpert eye - but I'm not an inference engine.

> - the subclass relationship
>   I take the reified rdfs:subClassOf triple in the example that has 
> circulated in earlier e-mail to be a response to a request to be more 
> formal, or more OWL like, in response to the powder-dr WD. However, the 
> design in the WD looks more user-friendly to me, if it could be made to 
> work ...
> - tools and motivations
> Why o why are we bothered?

Aye, there's the rub Mr. C.


[1] http://www.w3.org/TR/2007/WD-powder-dr-20070925/#structure
[2] http://www.w3.org/TR/2007/WD-powder-grouping-20071031/
[3] http://www.fosi.org/projects/powder/example4.owl
[4] http://www.w3.org/RDF/Validator/ARPServlet.tmp/servlet_14339.png
[5] http://www.fosi.org/projects/powder/example5.owl
[6] http://www.fosi.org/projects/powder/example5.png

Phil Archer
Family Online Safety Institute
w. http://www.fosi.org/people/philarcher/
Received on Friday, 14 December 2007 17:00:33 UTC

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