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Re: resources and URIs

From: pat hayes <phayes@ihmc.us>
Date: Fri, 18 Jul 2003 17:42:13 -0500
Message-Id: <p0600122fbb3dfcb27b2d@[10.0.100.23]>
To: Tim Bray <tbray@textuality.com>
Cc: www-tag@w3.org

>Well, I think we're making progress here.
>
>pat hayes wrote:
>
>>>The Web Architecture doesn't provide a way to talk about what 
>>>resources are or what they mean.
>>
>>Why does it even need to mention resources at all?
>...
>>>This is all very well and good, but it is neither necessary nor 
>>>appropriate that we pretend that the current architecture of the 
>>>web comprises any notion of "about-ness".
>>
>>Fine: but then please don't talk about semantics in the 
>>architectural description. Why do you even need to mention 
>>resources which the representations are 'of' ?? All the 
>>architecture needs to do is to ship representations around. Leave 
>>what they are 'of' to a semantic theory.
>
>From the point of view of Web Architecture as discussed in the 
>current draft, a resource is simply "that which is identified by a 
>URI".  This is highly consistent with the 2396 language "anything 
>that can be named or described".  I accept that this notion has 
>almost no semantic weight and is probably not essential to the 
>argument, but I don't think it's appropriate at this point for our 
>document to stop using the word "resource", which has been so 
>central to the web for so long.

OK, and I didn't seriously expect that it would. But let me push a 
little on that phrase "that which is identified by a URI". If, as you 
say, this is understood as being consistent with the 2396 wording - 
which is completely inclusive - then indeed anything can be 
'identified'. But in that case, can you elaborate a little on what it 
*means* to "identify" something? And what it means to say that 
anything can be "part of" an information network? And what relevance, 
indeed, network architecture of any kind can possibly have to a 
concept which is this inclusive? On this criterion, for example, 
Julius Caesar (http://www.perseus.tufts.edu/JC/ ) and Sherlock Holmes 
(http://sherlock-holmes.hypermart.net/sherlock.html ) are both 
resources; but surely they cannot be *part of* an information network 
(can they???)

>Maybe I'm missing something, but it seems to me that there ought to 
>be a smooth continuum between the Web of today, which says exactly 
>zero about resources other than they are identified by URIs, and the 
>Semantic Web, which addresses notions such as about-ness and 
>denotation.

Wait: the SW doesn't exactly address those issues, it *assumes* them. 
So do you, apparently, when you use the phrase "representation of". 
That is why it is so critical to get their senses right before we 
accidentally say something that we shouldn't.

And BTW, it is exactly that phrase "identified by URIs" which is 
giving me problems: I *still* don't know what it means: but Im pretty 
sure that what Dan Connolly takes it to mean isn't exactly what Roy 
Fielding means by it.  Dan's version is much more inclusive and 
all-encompassing than Roy's. For example, RFC 2396 says that once the 
resource has been identified from the URI, operations can be 
performed on it (the resource). Good luck performing operations on an 
active galaxy or an imaginary character.

>This leaves one severe friction point; let me try to expound it to 
>see if we are at least clear on the area of disagreement: webarch 
>currently says that URIs may be used to retrieve representations of 
>resources. Reading this according to the normal meaning of English 
>words causes me no stress

Me neither, but the rest of the text causes me stress, with that reading.

>: if you claim that an HTML page is a representation of the weather 
>in Oaxaca, I feel no discomfort.

Neither do I: but I do feel discomfort when I then try to also put 
together the claims that (1) the representation is OF the resource 
and (2) the resource is PART OF the information network.  Because 
with this reading, (1) implies that the resource must be the weather, 
and (2) then requires that the weather is part of the information 
network. At this point my ability to have this make overall sense 
fails me.

>  You, on the other hand, are profoundly disturbed by the notions 
>that (a) the weather in Oaxaca can be a resource, i.e. an object in 
>a networked information system

Yes, that seems like complete nonsense to me. Or at any rate, the 
only way I can make sense of it requires me to treat 'object in a 
network' as essentially meaningless. If anything can be 'in a 
network', including remote galaxies, tomorrow's weather and imaginary 
characters, then we aren't talking about network architecture in any 
sense I am aware of.

>, and (b) that an HTML page can be a representation of it.

I have absolutely no problem with the HTML being a representation, or 
its being a representation of the weather: in fact I think this is 
perfectly correct. I even don't have too much trouble with its being 
a representation of a resource (though I don't think that can 
actually make strict sense if taken literally). What I can't do is 
swallow all this together at once, particularly given all the other 
stuff said about resources..

>Do I have this straight?
>
>There is no way to know if it is correct or not since it doesnt seem 
>to mean anything that can be tested for truth.  Am I identified by a 
>URI? How could anyone possibly tell?
>
>You're right; the current web architecture provides no way to test 
>this condition.  I had (perhaps naively) understood that the 
>Semantic Web was going to give us the machinery to make 
>machine-usable assertions about semantic classes of resources and 
>their relationships.

The semantic web cannot possibly decide what the words you write are 
supposed to mean, surely? All I am asking for is some clarification 
of what it is that y'all are saying in these various documents. The 
words "resource" , "representation of" and "on the information 
network" are yours, not mine or the semantic web's.  Right now, I 
don't think anyone could make sense of what y'all seem to be saying, 
which is why Im making a fuss about it.

>>I don't think it does, in fact. That is, I think that it is 
>>necessary to make this distinction even to make proper sense of 
>>examples like the weather in Oaxala. If this distinction were not 
>>made, websites like 
>>http://www.wunderground.com/US/FL/Pensacola.html would be 
>>incompatible with the current TAG account of Web architecture, or 
>>else weather would have to be part of the information network.
>
>Here we part company.  That website makes perfect sense to me, and 
>if its owner wants to explain (in English) those pages as 
>representing the weather in Pensacola, that causes Web software no 
>heartburn.

Im not saying it does, and I can understand the website also.  I have 
no problems with the website. What I cannot do is make sense of *what 
the TAG architecture document says* when applied to this kind of 
example. The moral is not that there is anything wrong with the Web, 
but that the architecture document doesn't do a good enough job of 
explaining it.

>>If this is true, then please tell me what transfer protocol  and 
>>MIME type I should use for accessing the weather on the Web: not 
>>information *about* the weather - as you have made clear, anything 
>>to do with aboutness is not part of the architectural description - 
>>but the weather *itself*.
>
>You can't access anything on the web.  You can only dereference the 
>identifiers to get representations of that which they identify.
>
>>Fine, but what IS that sentence saying? What do y'all mean by "a 
>>representation of" a resource? In both the informal English senses 
>>and any technical sense I know of, that has to mean that the 
>>representation *represents* the resource. Apparently you do not 
>>mean that. So what DO you mean?
>
>The architecture defines a formalism.  In the formalism, there are resources

?? Do you mean that resources are part of a formal syntax?

>, about which we say effectively nothing

Unfortunately you say a great deal. You say that anything can be one; 
that they are all *parts* of a communication network, and that the 
representations are *of* them.  RFC 2396 says in addition that the 
URI enables you to access them and to perform operations on them. 
Taken together, it is hard to make these claims be mutually 
consistent.

>, identified by URIs on which we impose syntactic constraints. 
>Rules are provided for some URI schemes whereby protocols are used 
>to send and receive representations, formally specified as packages 
>of electronic information comprising metadata and payload.
>
>It is not that uncommon, in computer science, for formalisms to be 
>given names suggestive of their application-level usage; examples 
>would include "object", "method", "header", "interrupt", and so on. 
>From this point of view, the formalisms of "URI", "resource", and 
>"representation" are empirically observed to be sufficiently 
>well-specified as to serve as the basis for the successful 
>construction of software.

They are manifestly NOT adequate to this task when the software is 
obliged to process the representations *as representations*, ie in 
ways which reflect their intended meanings. There is a large body of 
technical literature, much of it in computer science, which uses 
words like "representation of" and "network" with some precision. All 
I have been doing is using that technical understanding to read your 
documents, and they don't then make overall sense.

If I can be brutally direct for a second, it seems to me that you 
need to be less complacent about this. You really do have a problem 
here.  It would be fine to just not say anything, and to defer all 
semantic talk to some other forum; but you do not do that, and indeed 
I have found that y'all seem quite determined to insist that all 
documents which mention URIs must include explicit wording which is 
clearly intended to make a semantical claim but is also at the same 
time hard to understand as meaningful when making such a claim.

>The English names for the formalisms strike me as sound, 
>rhetorically and tutorially.
>
>I think you are suffering entirely unnecessary angst from 
>overloading excessive semantic weight on what at the end of the day 
>are just labels for the parts of a successfully functioning 
>formalism.

Well, that is one possible conclusion, although how you can claim 
with a straight face that the weather is Oaxala is part of 
'successfully functioning formalism' I really cannot follow.   I 
would however then reserve the right to completely ignore all aspects 
of the document which refer to or use semantic ideas. This would 
include the words "resource", "identify" and the "of" in 
"representation of". If a semantical reading of these is "excessive 
overloading" then they are meaningless, and so can (and indeed 
should) be ignored by all responsible readers when considering 
further W3C specs.  If y'all would make a public acknowledgement of 
this point, preferably in the document itself, that would be 
extremely helpful.

Best wishes

Pat Hayes
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Received on Friday, 18 July 2003 18:42:21 UTC

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