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Re: [Fwd: RE: "information resource"]

From: Harry Halpin <hhalpin@ibiblio.org>
Date: Sat, 16 Oct 2004 17:27:44 -0400 (EDT)
To: "Roy T.Fielding" <fielding@gbiv.com>
cc: www-tag@w3.org, Mark Baker <distobj@acm.org>
Message-ID: <Pine.LNX.4.44.0410161649470.20287-100000@tribal.metalab.unc.edu>

Please note that in my original document I was using "representation" 
in the manner most people use it, not REST :)

The problem seems to all come from when the idea of resource is 
de-anchored from the Web so that a "resource" can mean anything. I have
no problem per se with that, but just am pointing out that some of 
the reasons people are looking into ideas such as "information 
resource" are because problems of authority and representation
are a lot trickier off the Web than on the Web, or when the two intermix
such as in the Semantic Web, where we have Web-statements about things
off the Web. 

I'm going to note that you seem to agree with me that the medical record
being modified is not just a representation of the same resource,
but a resource in its own right. 

> A representation is not some second-class object that doesn't
> exist outside of its original relation to the resource.  If the
> representation is modified then it is simply a modified representation,
> which is a *different* resource in its own right. The modification
> has no impact on the original resource unless an action is taken
> (directly or indirectly) on the original resource, after which its
> later representations will reflect the new state.

So, does it make sense to talk about the modified XML document qua 
resource as a representation of a resource, other than itself? And if the 
XML document is just a representation of itself, then
Representation = XML document
Resource = XML document

Why bother using the word Representation? Or using two levels of 
description? The representation gives you direct causal access to the
resource. The representation *is* the resource.  

Actually, it seems the problem is converse: a resource often seems like
a second-class object that doesn't exist outside of its original relation
to representations. On the Web, we know a URI identifies a resource. 
Off the Web, what identifies a "resource"? How do we know the original 
resource except through its representations, or in particular the representations that are 
authoritatively given? On the Web we know we have a resource when we have
a URI,and whoever controls that URI is obviously "authoritative".  Off the 
web it's unclear. When the two mix it's just tricky. For example, I have 
two medical records, one in Britain and one in the U.S. Whose more 
authoritative? And since I don't go to the doctor often, and the medical
record is supposed to be about my health, am I not the ultimate authority?
But then I don't have medical training....so, where's the clear resource
and representation distinction in that mess? It seems more a matter of
perspective than objective fact. Which is why it would probably be better
if the TAG stuck to "Web architecture" and remained as unclear as possible
about how this works off the Web. When the two intermix, as in the 
Semantic Web, ahhh...not really sure, that's why I think this idea of
"information resource" has come up off and on, along with things like
the tdb proposal and Henry Thompson and my ideas on WPNs. 

I think REST is a fine description of the Web, and have a lot of respect 
for it - it clearly works. As a philosophical theory of how the wide world 
outside the Web works it's probably not going to be perfect :)

On Sat, 16 Oct 2004, Roy T.Fielding wrote:

> On Oct 16, 2004, at 11:06 AM, Harry Halpin wrote:
> > I think Mark's point about the medical record can be turned around on 
> > its
> > head pretty easily. For example, a doctor may write on the note at time
> > t1, and this does not ofcourse effect an XML document made of the 
> > record
> > at an earlier point (t0). However, this can happen in reverse: the XML
> > document version of the medical record (t0) could be sent over the Net 
> > to
> > another doctor, who then writes another note on the XML document (at 
> > time
> > t2) that *is not* on the original note (t0). Does this mean that this 
> > new,
> >  updated XML document (t2) is still a "representation" of some
> > medical record (t0).
> For example, in all but the most high-tech hospitals, notes will be
> recorded on paper during the day and a clerk or nurse will enter
> the accumulated changes into the patient's record at some point
> during the day (or night).  Does that mean that the original resource
> is not the true medical record of the patient?  Yes, of course -- it
> is only the medical record as known by the provider of that resource.
> Is that a problem? Yes, and it is well-known in the field of medicine,
> which is why the US just authorized implantation of chips for storing
> medical records (of a sort).  It shouldn't be too hard to consider
> what that would mean if the chip is an RF-capable HTTP server that
> allows access to its resources under access control, perhaps
> even including resources that provide real-time monitoring of
> heart-rate, blood pressure, and blood sugar.  If you want to get
> really fancy, consider an embedded insulin monitoring system that
> is 99% self-sufficient aside from a configuration/monitoring
> interface with a virtual on/off switch.
> Those are all "information resources", but there is no effective
> difference between that class of resource and anything else that
> might be identified by a URI.  Arguing about their existence is
> a complete and total waste of time, since any system that relies
> on such a distinction is inherently broken and no better off than
> it would have been by accepting that resources are resources and
> assertions about nouns are usually ambiguous, requiring additional
> assertions to differentiate between terms.
> What makes a URI unambiguous is the degree of trust you can place
> on the naming authority to describe its meaning accurately and in
> a way that everyone understands and agrees to, and to maintain that
> meaning over all time.  Whether or not information is supplied by
> some system in response to a GET-equivalent request for that URI
> does not change reliance on the naming authority.
> > Even if the original (t0) is modified later (at t1)?
> > Is not the XML document (t2) *a medical record* in its own right, 
> > albeit a
> > different one from both the original(t0) and another modified 
> > version(t1),
> > in its own right? So I'm not sure how the use of the word 
> > "representation"
> > has any real meaning in this case, except in the technical sense that
> > for the XML copies (assuming they have URIs) an HTTP GET gets you
> > something. As the more philosophical use of the "representation" 
> > meaning
> > "a representation of", I think that use of the word only confuses 
> > things.
> No, you are simply assuming that the resource is one thing and
> then complaining when its representations do not actually correspond
> to that thing.  The assumption was wrong.  The data is a representation
> of something, even if that something isn't known to the requester.
> The reason for the word is because people constantly assume that
> performing GET on a URI transfers the resource itself, which simply
> isn't the case (even for a simple scheme like "file").
> ....Roy


	Harry Halpin
	Informatics, University of Edinburgh 	
Received on Saturday, 16 October 2004 21:27:46 UTC

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