W3C home > Mailing lists > Public > www-tag@w3.org > July 2003

Re: erratum Re: resources and URIs

From: pat hayes <phayes@ihmc.us>
Date: Mon, 21 Jul 2003 21:57:38 -0500
Message-Id: <p06001a0ebb424f554e80@[10.0.100.23]>
To: "Jonathan Borden" <jonathan@openhealth.org>
Cc: <www-tag@w3.org>

>pat hayes wrote:
>>
>>  >... I'd assume that it would return
>>  >a 404 ... BUT ... by creating the URI you actually do 'create' a
>resource.
>>
>>  Really? You do? Well, OK, if you say so.  But if it is that easy to
>>  create a resource then what do we need the Web for? I can write a
>>  simple piece of code which will generate syntactically legal URIs at
>>  an astonishing rate: am I creating resources?
>
>yep. what sort of resource do you suppose the URI urn:uuid:1233445523434
>identifies? (who knows)

You seem to be making my point rather than yours. I must not be following you.

>  >
>>  Seems to me that a more useful notion might be "actual information
>>  resource", which requires rather more effort to bring into existence:
>>  something that really can actually emit representations when pinged,
>>  something that costs real money and uses real energy.
>
>are you sure that it is the actual resource that emits representations

Yes.

>, or
>would you allow some machinery to emit representations on behalf of the
>resource?

Hmm. Maybe, but I would want that term 'on behalf of' made more 
precise within some architectural theory or framework.

>  I am not sure that the answer matters to me, its just that  I
>don't have a problem seeing an "oak tree" as a resource on whose behalf some
>computer might emit representations.

I have a  lot of trouble seeing an oak tree as something that can 
emit representations as a direct causal result of being sent a 
transaction token over some network. Its not totally impossible, I 
guess, if the tree had some unusual hardware attached to it ( a 
forestry experiment with C02 sensors on the leaves, something like 
that) but its pretty far-fetched; and it wouldnt give you a *picture* 
of the tree.

>
>>
>>  >It does 'exist' as the resource whose URI is
>>  >http://this.does.not.exist.com/index.html ... now Pat uses an example of
>an
>>  >address *for the physical world* which may or may not physically exist.
>In
>>  >URI space, as long as the URI is valid, the resource 'exists'. There is
>>  >nothing preventing the owner of 'exist.com' from creating such a resource
>>  >... the only issue I can see here is that since you don't own 'exist.com'
>>  >the URI you've created is 'illegal'. URI space as opposed to 'physical
>>  >space' contains a point for every legal URI ... such points might be
>called
>>  >'resources', and for every URI there does exist a resource (in URI
>space).
>>
>>  Well, that makes URI space into a purely theoretical construct,
>>  right? Now, what theory does it serve any purpose for??
>
>The purpose of this description is as an _analogy_ to physical space.
>
>>What theory -
>>  and what *kind* of theory - requires us to hypothesise this virtual
>>  URI space of virtual resources? We don't need it for semantics - in
>>  fact, its does more harm than good - and I can't see why we need it
>>  for an architectural theory, since it plays no role in the
>>  architecture. In fact, it strikes me as just a piece of nonsense made
>>  up to seem like a theory, which has become a kind of doctrine that
>>  must be defended at all costs and is beyond the reach of reason.
>
>Ok, so evidently you don't find this a useful analogy, but I've never called
>this a theory, just a way of explaining the terminology 'exists on the Web'.
>We aren't talking metaphysics here, just local lexicon.

How very like the people I argue with to use 'metaphysics' as a term 
of dismissal. As you know, my job is to try to help get semantics 
straight. This does involve something awfully like metaphysics, in 
fact. If y'all don't give a damn about metaphysics, fine: but please 
keep out of the kitchen, because I AM talking metaphysics, and sloppy 
analogies aren't any more help here than they would be in network 
engineering or, say, neuroanatomy.  "Exist" is a technical term with 
a remarkable sharp meaning. If you don't mean it, don't use it.

To go back to your analogy: every URI has a corresponding thing in 
'resource space'. The mapping is 1:1 and onto (no resources without a 
URI; every URI has a resource). The *nature* of resources is not 
discussed and plays no role in the theory. OK, so why not make this 
be the identity map, and say that the URIs *are* the resources? That 
simplifies the theory, apparently causes no problems and saves a lot 
of interminable discussion about the nature of nonexistent entities.

>,>
>>  >We might similarly say that "1404 West La Rua St., Pensacola" is an
>>  >_invalid_ address per the rules of either the postal service or of
>>  >Pensacola, FL ... just as per the rules of "exist.com"
>>  >http://this.does.not.exist.com/index.html might be invalid.
>>
>>  Right, but it is invalid precisely because if you follow the rules
>>  for dereferencing postal addresses, you will find that there is no
>>  such place (it would be in the middle of a large cemetery). In other
>>  words, the 'resource' - in this case, the building at that address -
>>  *does not exist*.
>
>Right, the building *does not exist* in the physical world -- you are using
>an invalid address.

Right.  Just as there may be no such resource to be indicated by the 
URI: the resource may not exist.

>The point is that presumably the city of Pensacola is
>somehow responsable for assigning addresses to buildings in Pensacola. All
>that I was saying is that similarly the owner of 'exist.com' (who can be
>found via whois) is responable for assigning URIs which are under the DNS
>entry 'exist.com' to resources whose representations are available at
>'exist.com'.

Suppose that said owner fails to live up to his responsibilities. 
Does the URI then identify a resource? How? What?

>
>>
>>  BTW, this example is close to my heart because of an amusing
>>  incident. My local cable company mistyped my address and sent my
>>  bills to this non-address (mine is *east*, not *west*). The post
>>  office simply trashed them and didn't tell anyone (no 404 errors). I
>>  never saw them. The cable company sent demands, then threats, then a
>>  technician to cut off my service.  The technician, finding the
>>  graveyard, reported that there was no service to that address. Then
>>  the debt collection agency sent even nastier threats, all to this
>>  nonexistent address; I had no idea this was happening.  Eventually, a
>>  store in California refused to accept my credit, and the subsequent
>>  enquiries uncovered the trail of uncorrected confusions. It will take
>>  7 years to get this mess off my credit reports. Now, should I console
>>  myself by saying, Ah, but there really *was* a resource there - a
>>  kind of Platonic building in the graveyard that nobody could see,
>>  brought into existence in Address Space just by the typo on the
>>  envelope;  its just that those postal guys weren't able to do the
>>  dereferencing? Somehow, that doesn't seem to help.
>t
>No, that is the whole point. You see, the problem is not that the resource
>wasn't there -- it could be an abandoned building, the problem was that the
>address was incorrect.

No, the problem was *precisely* that the resource wasn't there. If it 
had been, the owner might have written 'not at this address, return 
to sender' on the envelope and handed it back to the mailman.

>The problem was that someone attached an invalid
>address to *you*.

Hmm. Lets see now, does that make sense? If the address really had 
been attached o me, wouldn't I have got the letters? Surely the point 
is that the address wasn't attached to *anything*.  It was a 
perfectly well-formed address, and the delivery protocols (sorting, 
putting into the right bag, etc.) all would have worked fine; its 
just that when you go there, there's no there there, as some writer 
might have said. Like a URI which doesn't identify any resource.

>On the Web, folks are trying to mitigate these issues by
>placing the responsability for assigning URIs to web resources on the owner
>of the DNS name of the URI (for HTTP URIs) etc. This issue, as you
>illustrate, has little to do with URIs in specific, rather that bad
>addresses, like bad identifiers, cause real problems.

But if it is taken as axiomatic that all URIs must identify a unique 
resource, as you and the TAG document claim, what does 'bad address' 
mean? All addresses are equally good, on this account: the difference 
between bad and good has been defined out of existence.

>
>>  >
>>  >In the Web Architecture, you never can actually get your hands on the
>>  >resource, rather the representation.
>>
>>  Is that really correct? Seems to me that you - or maybe the Web
>>  itself - does 'get its hands on' an actual information resource
>  > indicated by the URI, and that very thing then emits the
>>  representation. Isnt that (a sketch of) the Web architecture for all
>>  the ...TP protocols?
>
>If you consider:  HTML representation -isRepresentationOf -> document
>resource
>then yes. But if we consider, alternatively,
>
>document -isRepresentationOf-> weather in Oaxala
>
>then no.

Yes, Sigh. But which is it? That is exactly what I am trying to find out.

>
>The 'resource' need not physically 'emit' the representation, an HTTP server
>acts as a proxy for the resource. Is that way of describing things a
>problem?

If 'proxy for' and 'denotes' are supposed to be synonymous, then yes, 
of course it is a problem.

>In this view the HTTP server is the RPC endpoint, or Sandro's
>ResponsePoint for the representation. Analogous to RPCs, the proxy is for
>the remote 'object' which would be the resource itself

OK, I agree the simple 'address' metaphor isnt able to handle the 
full network-engineering subtleties of proxies, endpoints and so on. 
Still, there is a basic distinction between the thingie, howsoever 
complicated and virtual, which in some sense emits the 
representations in response to a network request, and the subject or 
topic or referent of the representation itself. The TAG architecture 
document uses the phrase 'representation of' in senses that can be 
understood either way.  Which of these does it mean??

>-- and note that many
>such resources are read only :-))

Thats irrelevant.

Pat
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Received on Monday, 21 July 2003 22:57:42 UTC

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