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

Re: HTTP URIs and authority

From: Pat Hayes <phayes@ihmc.us>
Date: Wed, 24 Oct 2007 11:43:52 -0500
Message-Id: <p06230905c34523cc8e72@[10.100.0.19]>
To: noah_mendelsohn@us.ibm.com
Cc: Alan Ruttenberg <alanruttenberg@gmail.com>, Mikael Nilsson <mikael@nilsson.name>, Richard Cyganiak <richard@cyganiak.de>, wangxiao@musc.edu, W3C-TAG Group WG <www-tag@w3.org>

>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.

>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.

>  It seems to follow
>that in the case of conneg, the resource must in some sense be (or be
>isomorphic to) the union of all served representations.

Maybe not union: something more subtle. I havnt thought about that 
hard enough yet to try stating it. I think it might need to refer to 
the representation that would have been sent if you had asked for a 
different content (eg imagine a clock which can give you a jpeg 
clockface or a digital time: when you GET the digital, then the 
clockface you WOULD have gotten just then IF you had asked for it 
should have been correct as well.)

>  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:

http://www.ihmc.us/users/phayes/central_plain_turn.jpg

is in fact Moby Dick, but I've decided to send you a non-isomorphic 
webarch:representation of it. Why not? Who gets to decide the 
representation policy?

Pat

>Noah
>
>--------------------------------------
>Noah Mendelsohn
>IBM Corporation
>One Rogers Street
>Cambridge, MA 02142
>1-617-693-4036
>--------------------------------------


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Received on Wednesday, 24 October 2007 16:44:06 UTC

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