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Re: New Editors Draft of the httpRange-14 Finding

From: Alan Ruttenberg <alanruttenberg@gmail.com>
Date: Fri, 24 Aug 2007 12:56:58 -0400
Message-Id: <AFA909B0-4EB4-459A-BFF3-74E7D34F47B1@gmail.com>
Cc: "'www-tag'" <www-tag@w3.org>, "'Jonathan Rees'" <jar@creativecommons.org>
To: Rhys Lewis <rhys@volantis.com>

On Aug 24, 2007, at 3:53 AM, Rhys Lewis wrote:

> Hello Alan,
> My impression is that the language in AWWW is deliberately that way  
> because there is no hard and fast rule about what defines  
> 'equivalent' representations. I suppose that we might say that  
> authors make assertions about equivalence when they create multiple  
> representations and offer them via content negotiation.

It's ok if they make the assertions. But there needs to be a way to  
see that they make sense (at least if the plan is that the SW is to  
be used for science).

>  By the way, I'm not convinced that lossless transformation is the  
> right model for this. For example, I believe that representations  
> that differ only in language are appropriate to serve via content  
> negotiation. HTTP is explicitly set up to support language as one  
> of the criteria for such negotiation [1]. The HTTP specification  
> notes that the reason it's called content negotiation and not  
> format negotiation is precisely because representations are not  
> necessarily different formats of the same content.

I didn't offer it as the right definition, just as an example of  *a*  
definition, which "representation" currently lacks.

>  Actually, there are some intersting use cases in accessibility and  
> in support for small mobile devices that are related. Suppose I  
> mint a URI and assert that it identifies a resource that let's you  
> find a barbeque I'm holding this weekend (chance would be a fine  
> thing with the summer we've had!)

That's a nice example. The resource is "a thing that lets you find a  
barbeque". This measures the information content as the outcome of  
the agent evaluating the instructions. Is that a commonly accepted  
idea about what an information resource is?

>  Anyhow, for users with traditional Web access, I provide a  
> representation that includes a map, delivered as a large, colour  
> image, with a big arrow showing the location. If I want to support  
> users with visual disabilites, or people accessing my site with a  
> small, text only mobile phone, this won't be much use. I might want  
> them to receive directions to the event instead. I might deliver  
> them as text or even as an audio clip.

Are these the same information resource? Or different answers to the  
same question?

>  Now, the question is, can I legitimately serve the map, the  
> textual directions and the audio as representations of the same  
> URI? If I claim that the URI identifies a map of the location of  
> the barbeque, then I think the answer is no. However, if I claim it  
> identifies a resource that let's users find the barbeque, I suspect  
> the answer might well be yes, though I would not be surprised to  
> find that opinions differ.

I'm happy with any definition that is operational and can be  
consistently applied.

>  In short, I think equivalence is in the eye of the author.

We're going to have a real communication problem on the semantic web  
if we don't fix that.

>  On the specific question of whether a jpeg is a representation of  
> a person, I think the consensus is no. There has been a lot of  
> discussion about related topics on this list over the last couple  
> of months. If you mean person the way I think you mean it, then  
> that would be a non-information resource, as described in AWWW.  
> These have no representations and the current feeling is that it  
> would be misleading to serve a representation if the associated URI  
> is accessed. The range-14 finding is about what should be returned  
> if such an access occurs.

There is an issue that I'm betting will bite. You 303 to a CN manage  
URI. There will be temptation to allow (to take your example) image/ 
jpg return a picture in response to http://www.example.com/ 

Is this allowed, along with the rdf and html versions? If so, what is  
the IR that these are all representations of. If not, how does one  
associate a picture to the non IR?

It would be good to explicitly clarify this in the note.

More comments forthcoming at some point.


> Of course, you could content negotiate between a jpeg, gif, png... 
> (pick your favourite image format) for a URI that you claim is a  
> picture of a person.
> Best wishes
> Rhys
> [1] http://www.ietf.org/rfc/rfc2616.txt (Section 12 Content  
> Negotiation)
> From: Alan Ruttenberg [mailto:alanruttenberg@gmail.com]
> Sent: 24 August 2007 05:48
> To: Rhys Lewis
> Cc: www-tag; Jonathan Rees
> Subject: Re: New Editors Draft of the httpRange-14 Finding
> Hello Rhys,
> The problem I have always had is knowing what the conditions are  
> for two representations to be of the same resource (and are the  
> resources information entities, or only the representations? - can  
> I content negotiate for the jpeg "representation" of a person?)
> Using translations as an example is particularly problematic, as  
> most language translations are not exact because there are  
> inevitably cultural attachments to the words that can not be easily  
> understood by non-native speakers.
> I can understand some much more constrained than what I perceive to  
> be extremely loose language the AWWW, and this document as well,  
> use. For instance we could say that two representations are of the  
> same resource if there is a documented algorithm implementable by a  
> computer that losslessly transforms one into the other, as with a  
> byte sequence and its gzip compressed version.
> My worry has been that unless there is some way for someone to say:  
> "No, you are wrong, these two things are *not* representations of  
> the the same thing" then the term "representation" is meaningless.
> Regards,
> Alan
> On Aug 23, 2007, at 3:00 AM, Rhys Lewis wrote:
>> Hello everyone,
>> Could I just take a moment to thank Roy and David for their  
>> extensive comments on the latest draft. They provide excellent  
>> input for the forthcoming TAG face to face meeting next month.
>> I hope to make progress on specific points before that meeting. If  
>> so, I'll respond here on particular topics.
>> Thanks again
>> Best wishes
>> Rhys
Received on Friday, 24 August 2007 16:57:09 UTC

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