W3C home > Mailing lists > Public > www-tag@w3.org > October 2007

Re: HTTP URIs and authority

From: Xiaoshu Wang <wangxiao@musc.edu>
Date: Wed, 24 Oct 2007 19:57:31 +0100
Message-ID: <471F959B.3070202@musc.edu>
To: Pat Hayes <phayes@ihmc.us>
CC: noah_mendelsohn@us.ibm.com, Alan Ruttenberg <alanruttenberg@gmail.com>, Mikael Nilsson <mikael@nilsson.name>, Richard Cyganiak <richard@cyganiak.de>, W3C-TAG Group WG <www-tag@w3.org>

Pat Hayes wrote:
>> Pat Hayes wrote:
>>>
>>>> Pat Hayes writes:
>>>>
>>>>>  > [Noah Mendelsohn wrote]:
>>>>>  >  If I say that it's for the poem, and in a year or so someone
>>>>>  >comes up with a font I like better, I see no problem with my 
>>>>> changing
>>>> the
>>>>>  >page to use that.
>>>>>
>>>>>  Neither do I: but that doesn't mean that the URI denotes anything
>>>>>  font-less, like the 'real' poem. It just means that your resource
>>>>>  here has a changing font.
>>>>
>>>> Let's make the example more complicated.  I mint the URI and claim, at
>>>> least insofar as you're willing to allow me too :-), that it 
>>>> represents
>>>> the poem itself, not a particular presentation of it.  Because I'm 
>>>> a cool
>>>> Web guy, I support content negotiation.  On day one, in addition to 
>>>> that
>>>> fancy 25 point italic version served as text/html, I also offer
>>>> text/plain, with each line of the poem given on one line of the 
>>>> returned
>>>> text.
>>>
>>> Thats still a particular document inscription of the poem, not the 
>>> poem itself.
>>>
>>>>  Now, as in the first example, I decide I've found a better font for
>>>> the HTML, and I leave the text version unchanged.  You seem to 
>>>> imply that
>>>> the resource itself has surely changed?
>>>
>>> Something has changed, yes. I'm presuming that was the resource in 
>>> question, no? Its a small change, admittedly, but it is a change.
>> You seems contradicting yourself here.  User your term, the "document 
>> inscription" has changed, the peom has not.
>
> No, I'm here assuming the overall webarch framework and terminology 
> (which I think you do not), according to which it is (literally) 
> impossible to put an actual poem at an http endpoint, so the 
> 'resource' being talked about here is an inscription in html, or a 
> complex of such inscriptions in various fonts. It is an 'information 
> resource'.
It is factually impossible, that is what I want to say.  What you get 
back, at most, it is a *copy* of the resource because the bit on your 
server is a different one than the bit on my laptop?  But even that, we 
don't know about it without any additional assertions.  And this extra 
assertions, if you want, make the resource different from 
representation.  So, what a URI denotes is always an abstract thing, 
what you categorized as "representation-3" yesterday.  You can never get 
it back, you can get back "representation-2" a.k.a. REST:representation 
and try to figure it out representation-3, a.k.a "resource" from 
"representation-2".
>
>>>> Your view seems to be that the resource needs to, at least in some 
>>>> sense,
>>>> be isomorphic to the representation, so you infer that when the
>>>> representation changes the resource must have changed.
>>>
>>> Well, that last point doesn't need the isomorphism assumption 
>>> exactly. But yes, I'm assuming that webarch:representation is 
>>> something like taking an imprint from a platen. It has to in some 
>>> sense be a 'faithful' representation of 'all' of the resource. I 
>>> agree this needs to be said more carefully to allow for content 
>>> negotiation.
>> Then, in that case, the scope of URI must be scaled back to our file 
>> systems.
>
> For information resources, yes. But those are all things that already 
> fit into our file systems.
>
>>   Who is there to judge "faithful"?
>
> True, true. Which is one reason I don't like the webarch usage of 
> "representation". But let us say that what counts as 'faithful' should 
> be determined by the content type. For HTML it is clear: it would not 
> be acceptable for example to return only the first half of the HTML on 
> a web page, or every other line, on the grounds that this was just an 
> alternative kind of 'representation' of the HTML source.
But that is just your perception, or our misuse, about the term 
"representation", what if we substitute it as a "message", would that 
make it clearer?
>>>>  My preferred view
>>>> is that there is allowance for changing policy as to how a particular
>>>> resource is represented, and that such changes to not necessarily 
>>>> imply
>>>> that the resource itself has changed.
>>>
>>> Well, that is a coherent position, I admit, but I don't like it, as 
>>> it seems to reduce the webarch notion of 'representation' to 
>>> vacuity. If I can change my resource without its 
>>> webarch:representations changing, what *is* the relationship between 
>>> the representation that GET delivers and the resource itself? It 
>>> isn't, apparently, determined by HTTP or by media type or content 
>>> negotiation. In fact, its not determined by anything at all. So it 
>>> can be anything at all. I could say that this resource:
>> Resource owner and URI owner are two different entities.
>
> Well, OK, but who owns Moby Dick? 
Does it matter who? We know it is likely different from a URI owner, if 
there is one.  No one said that a resource owner has to have a 
relationship with the owner of a URI that denotes that resource?
> Or change my example so that the jpeg URI denotes, I will say, a paper 
> I wrote (and own the copyright of), say the dialog to be found here:
>
> http://www.ihmc.us/users/phayes/Dick&Ray.html
>
> Now, what's to stop me claiming that the image is just a rather 
> unusual representation of the text? According to Noah, I can choose my 
> own 'style' for my representations. But this seems silly to me.
Exactly. "http://www.ihmc.us/users/phayes/Dick&Ray.html" identifies a 
resource, not the HTML representation rendered on my browser.  You sure 
can have an image representation of that paper, why not?
>>   The URI owner gives you his/her *representation* of the resource. 
>> For a given resource, there can potentially have multiple URIs, when 
>> grounded to the web, someone will provide a better representation of 
>> the resource than the other.  Eventually we choose those better ones 
>> and disregard the rest. Doesn't this sound right?
>
> Well, but now you are raising a different point. That does sound nice, 
> but the problem I have with it is how to know which of the 
> representations is best. We have literally NO access to the actual 
> resources, and if representations can have arbitrary 'stylistic' 
> differences, then we can't rely on any fixed semantics. So we would 
> seem to be lost in a cloud of unknowing.
You open the package (representation) and comprehend for yourself.  
Isn't this how we observe the world? We observe the world by light, 
sound, order, touch...all of them is just one of those 
*representations*, what makes it so hard to understand if the 
information is carried in a bit-stream?  Besides, do we have to be in 
the past to know the past? We choose what to believe, right?  Just like 
the current Iranian president chooses not to believe there is a 
holocaust, can you do anything about it?

Regards,

Xiaoshu
Received on Wednesday, 24 October 2007 18:58:28 UTC

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