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RE: Question on the boundaries of content negotiation in the context of the Web of Data

From: Williams, Stuart (HP Labs, Bristol) <skw@hp.com>
Date: Thu, 12 Feb 2009 13:53:25 +0000
To: Michael Hausenblas <michael.hausenblas@deri.org>, "www-tag@w3.org" <www-tag@w3.org>
Message-ID: <233101CD2D78D64E8C6691E90030E5C8293C588F02@GVW1120EXC.americas.hpqcorp.net>

Hello Michael,

<snip/>

> Please note that I don't ask if this works. It does. Obviously. The
> question, to put it in other words, is: is the PNG *representation* derived
> via conneg from the generic resource <http://sw-app.org/sandbox/house>
> equivalent to the RDF in Turtle?

Does't look like it to me...

> If not, why not?

The 'house' depicted in the PNG appears to have a red roof. The redness of the roof (amongst may other properties of the 'house') are not apparent in the turtle.

The only possible coherent fragment of information that could conceivably be the same between the two representations is a subject URI. In the case of the PNG (not that I'm familiar with the internal encoding of information - particularly if its more structured than an array of coloured dots or a list of lines, shapes and fills) whilst a human interpreting the picture might intuit that the juxtaposition of what appears to be a text string close to what appears to be a 'house' may be intended as naming the house with the string and that that named thing is the subject of, well what, I suppose the art, if we can call it art :-). However one is quite some distance from a machine readable assertion that http://swa-app.org/house.tll#my names any particular thing far less a house. There is also the question of what the media-type registration for PNG has to say about what the fragId should be interpreted as referring to; I don't know, I haven't looked.

The turtle representation, gives a machine readable assertion that claims http://swa-app.org/house.tll#my as a http://swa-app.org/house.tll#House (whatever one of those is).

> If it is, can you please point me to a finding, note, a
> specification, etc. that 'normatively' defines what 
> 'equivalency' really is?

Do you think those representations are equivalent representations of whatever it is that you intend http://swa-app.org/house.tll#my to be an identifying URI of - (a conceptual red roofed house? a depiction of that concept? an actual particular house?... )

Equivalent for ALL purposes? or just for some narrowly defined purpose?

I guess that it could be argued that the subject of both representations is the same 'house' - but they are representations of two different descriptions/depictions of the same thing. IMO you shouldn't be conneg-ing between these at all. One might wriggle and provide a ttl representation that used some drawing vocabulary to describe the lines and shapes in the picture, adn I think given such a vocab - it would be reasonable to regard a PNG and such a detailed ttl account in a suitably grounded vocab - as equivalent representations of a depiction of... well, a house (if that's what it is).

BTW: what is it about the depiction that makes it a depiction of a house - quite apart from web architecture, what are the rules for examining two depictions/pictures and determining them to be equivalent? An if you can resolve that is the ttl representation an admissable equivalent under those rules?

> Cheers,
>       Michael
> 
> -- 
> Dr. Michael Hausenblas
> DERI - Digital Enterprise Research Institute
> National University of Ireland, Lower Dangan,
> Galway, Ireland, Europe
> Tel. +353 91 495730
> http://sw-app.org/about.html

Regards

Stuart
--
Received on Thursday, 12 February 2009 13:58:33 GMT

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