W3C home > Mailing lists > Public > www-tag@w3.org > April 2008

Re: Uniform access to descriptions

From: Xiaoshu Wang <wangxiao@musc.edu>
Date: Wed, 09 Apr 2008 11:01:21 +0100
Message-ID: <47FC93F1.4020803@musc.edu>
To: Pat Hayes <phayes@ihmc.us>
CC: "Williams, Stuart (HP Labs, Bristol)" <skw@hp.com>, Jonathan Rees <jar@creativecommons.org>, "www-tag@w3.org WG" <www-tag@w3.org>, Phil Archer <parcher@icra.org>

Pat Hayes wrote:
> At 10:28 PM +0100 4/8/08, Xiaoshu Wang wrote:
>> Pat Hayes wrote:
>> <snip>
>>> OK, I take your point: that you don't disagree with me here, but 
>>> instead take the view that/ nothing/ satisfies the TAG criterion for 
>>> an information resource, at least as stated by them: "its essential 
>>> characteristics can be conveyed by a message"; so the entire 
>>> discussion is moot, since by the published criterion, according to 
>>> http-range-14,/ no/ http request should/ ever/ return a 200 code. 
>>> Which is ridiculous, etc.. But here, I simply disagree with you. At 
>>> best, I think what you have shown in 
>>> http://dfdf.inesc-id.pt/tr/web-arch is that the published definition 
>>> of 'information resource' is faulty. Perhaps so: along with a lot of 
>>> other people, I also don't like it. But surely the/ intention/ of 
>>> the TAG was reasonably clear. When a browser accesses something we 
>>> informally call a 'web site' and gets a 'web page' back to display 
>>> to its user, clearly said 'page' is a reasonably close facsimile 
>>> (which is, again informally, what webarch-representation seems to 
>>> mean, most of the time) of/ something/, and moreover that something 
>>> has a number of familiar properties: it is located on its server, it 
>>> can respond to http requests, it might well have been written in 
>>> HTML, and so on. We all know this and also know, in a 
>>> pre-philosophical sense, what is being spoken about. We also know 
>>> that it is very hard to give a single definitive characterization of 
>>> these things that we can engage with over the internet, partly 
>>> because the technology keeps changing under our feet and extending 
>>> the possibilities in new ways. Nevertheless, without splitting hairs 
>>> about the exact boundaries of this elusive concept, we can all 
>>> recognize and largely agree on a number of clear-cut example and 
>>> non-example cases. Webpages and jpeg images are examples. HTML 
>>> documents are examples. Non-electronic physical objects and abstract 
>>> or fictional entities are clearly non-examples. The TAG bravely, or 
>>> perhaps foolishly, tried to give an actual definition: but rather 
>>> than seize on this and use it to attack the intention seems, even if 
>>> its good philosophy, not to be the most useful way to proceed. 
>>> Better to take the intention and use it to attack the definition :-)
>> Sure, we can take an informal definition.  But the issue becomes 
>> serious when the TAG intend to invoke such logic.  That is: if _:x 
>> HTTP-200 => _:x a webarch:IR.  The question was raised with good 
>> intention because if without such logic, what is the point of 
>> httpRange-14?
> Fair enough.
>> Then, here is the dilemma: If I publish something in RDF, I must 
>> worry if something is an IR or not.  Because in logic, a single 
>> contradiction will invalidate the entire theory.
> Not on the main path, but I disagree with you here also. Logic 
> basically gives up when faced with an inconsistency, but that does not 
> imply that one inconsistency makes the entire theory useless. There 
> are many ways to isolate or ignore contradictions which can be 
> deployed in practice. But still, I agree we should try to get it right 
> wherever possible.
>>  Hence, I must know precisely the definition of IR in order to ensure 
>> that my data won't (unnecessarily) lead to such contradiction. But I 
>> cannot do that with the current definition.
> But you can in many (most?) cases. Here's what you do. You have a URI 
> and something in mind you want it to denote. Now, give that URI to a 
> browser and see what happens. If you get a 404, the URI is yours to 
> command. If you get a 303 then its still yours, but it would be good 
> manners to make it denote something connected with the result of the 
> 303 somehow. If you get a 200, then you ask yourself the following 
> question: is/ whatever sent me this response/ the very thing I have in 
> mind that I want my URI to denote? If the answer is yes, go ahead. If 
> not, use a different URI or (if you can) alter the response it returns 
> when GETted.
How do I judge that *many(most)*.  The web - and semantic web - is 
essentially want to take care of one thing - that is to make the meaning 
of ad hoc communication as clear as possible.  This ambiguous many(most) 
is, in fact, resulted from the ambiguous definition of IR, isn't that so?

Let's me use this analogy, when you received a mail (or email, such as 
this), do you judge its content by *how* it is delivered to you? I don't 
know about you, but I don't. 
> My point is that this is all that http-range-14 really/ requires you 
> to actually do/. You can ignore the metaphysics and the confusion and 
> the definition-soup and so on.
>> Then, since I can always be accused wrong regardless of my best 
>> intension,
> Well, you can be accused, but it seems to me that the above algorithm 
> also gives you a good defense. Remember, you never have to justify a 
> claim that something is an information resource, only that it isn't.
If I don't know what is an IR, how do I judge what it isn't?  This is 
essentially what Tim responded to my question.  He said: well !IR <> 
non-IR.  Then, what is the intersection of IR and non-IR.  This is not 
an answer, this is to avoid answer and then it is useless, don't you 
think so?
>>  what is the point for me to use 303 instead of 200?  The latter is 
>> cheaper and easier. If eventually, everyone has felt the same dilemma 
>> that I felt and choose 200 anyway, then by public verdict, 
>> httpRange-14 becomes useless.
> Well, true, but I don't see that happening, in fact. My own private 
> conclusion is that http-range-14 makes sense, but the moral I draw 
> from it is to never, under any circumstances, use an unhashed URI to 
> denote anything but a webpage or a deliverable document of some kind. 
> Which is a kind of conformity by avoidance, but much simpler to 
> satisfy than trying to mess around with 303 codes.
Use *unhashed URI* is what TBL proposed.  As I said before, it can 
work.  But it works is not by answering httpRange-14 or the definition 
of IR, but by - as you said - *conformity by avoidance*.  This again 
showed how bad the definition of IR is.  httpRediction-57 is the same 
thing to *conformity by avoidance*.  My solution is to simply ignore it 
because we cannot hide forever.

If we take TBL's view + httpRange-14, then any "slash URI" cannot be 
discussed with "hash URI". Unless, we give IR a syntactic definition, 
i.e., any resource denoted by a URI ended with a slash.  But this again 
makes any 200->IR irrelevant, right?
>> On the other hand, if we don't invoke the earlier introduced logic, 
>> what is the point of httpRange-14?
> See above.
>>>> In this sense, any HTML page is abstract with respect to the web.  
>>>> What is concrete to the web is the "representation" of the resource.
>>> Not in the webarch sense of 'representation'. Those 
>>> 'representations' are transient entities which exist only as they 
>>> move across the physical Web in an http (or xxxtp) response message. 
>>> They are like the photons of the Web: we become aware of them only 
>>> when they have already ceased to exist, by causing changes to our 
>>> relatively static data structures.
>> It is!  What is parsed in your browser is the *representation* of the 
>> resource denoted by that URI, which is always abstract w.r.t. to the 
>> web-architecture.
> My browser is/ sent/ a representation, but it then creates something 
> else in my RAM which I get to view and store away for later. Or at 
> least that is my understanding of the official story about 
> webarch-representations.
>>  We always understand reality from its representation. What I 
>> perceived you is not you but your representation in my brain.
> Well now we are doing real philosophy, but that is wrong. My 
> perception (of, say, a tree I am looking at) is maybe constituted by 
> representations in my brain, but what I/ perceive/ is the actual tree. 
> We cannot, in fact, perceive our own mental representations: if we 
> could, cognitive science would be a lot easier than it in fact is.
>>  When you dereference http://dfdf.inesc-id.pt/tr/web-arch, you didn't 
>> get that resource, you get a *representation* or *description* of 
>> that resource.
> Not a description, but a webarch:representation of it, yes. But I got 
> that/ from/ the actual resource. It was the resource that sent it to 
> me. (If there hadn't been a resource there to send it, I wouldn't have 
> got it; just as if there hadn't been a tree to bounce photons off, I 
> wouldn't have my mental representation of the tree.) And it is the 
> resource which sent me the representation that (in the case of a 200 
> code, according to http-range-14) the URI denotes, not the 
> representation that it sent.
Not really.  Let's me give you this example.  Take two colors Red and 
Green as an example. Can you give me a proof that what I *called* Red is 
actually what you perceived Green and vice versa?  In other words, if 
you can distinguish model 1 from model 2?

Model 1: Green(xiao:Red= pat:Green) Red(xiao:Green=pat:Red)
Model 2: Green(xiao:Red= pat:Red) Red(xiao:Red=pat:Red)

If you cannot, it therefore proves that the actual reality (such as 
Green and Red) is always unknown and is in the eye of beholder.  But 
does what reality actually is matter?  It does NOT.  What matters is 
*the consistency* between our descriptions about the same reality. 
>>>> Or we can take TBL's viewpoint.  To make all slash URI as an 
>>>> information resource.
>>> The URIs aren't the information resources themselves: the i.r.'s are 
>>> what are/ denoted/ by the slash URIs. And that's not really an 
>>> architectural decision: its more of a rule of semantic 
>>> interpretation. And I (now) think that its the only practical rule 
>>> to adopt in this case, if we have to have any rules at all. And all 
>>> the rest of the decision follows from that.
>>>>  This again gives IR a syntactic definition, which is O.K. and 
>>>> usable.  But the reality that many hash URI are used in a way that 
>>>> will make TBL's position difficult to accept.
>>> ? Really? But it seems to me that this position is entirely/ 
>>> agnostic/ about the meaning of hash URIrefs. Which indeed is one of 
>>> its strengths.
>> Do we know what a #URI denote?
> No
>> Is it an IR or not?
> We have no idea. It could be anything, just as a 303 redirect tells us 
> nothing about what the URI is obliged to denote. Http-range-14 is 
> silent on both of these cases. It only specifies that/ in the case of 
> an unhashed URI returning a 200 response/, the URI is understood to 
> denote the resource that emits the response.
>> Or something-else? For instance, what does this URI denotes?
>> http://dfdf.inesc-id.pt/tr/doc/web-arch/img/fig2#rsc
> The only way to tell, is to find out what assertions are made using 
> this URI by sources you are inclined to trust, and go from there. Not 
> a very informative answer, I know, but I don't think that it is 
> possible to give a more informative one, so we will all have to try to 
> get along with this.
>> Just remind you that there are a few mime-type for 
>> http://dfdf.inesc-id.pt/tr/doc/web-arch/img/fig2 (text/plain, 
>> text/html, image/svg+xml, image/jpeg, and image/gif).  This is an 
>> area that TAG hasn't been able to address yet.  But again, it can be 
>> consistent if we assume that a URI always denote an abstract resource 
>> and *representation* is what you get.
> Im not sure what you mean by 'abstract resource'. For example, I am 
> pretty sure that I am myself not very abstract at all.
Abstract means there is always something potentially unknown about the 
resource.  What we get - a description (or representation) - could be an 
asymptotically close one but never the one.


Received on Wednesday, 9 April 2008 10:02:15 UTC

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