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

Re: erratum Re: resources and URIs

From: Jonathan Borden <jonathan@openhealth.org>
Date: Mon, 21 Jul 2003 14:47:35 -0400
Message-ID: <017d01c34fb8$90b73b50$b6f5d3ce@svhs.local>
To: "pat hayes" <phayes@ihmc.us>
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)

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

>
> >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.

>
> >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. 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'.

>
> 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.

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

> >
> >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.

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

Jonathan
Received on Monday, 21 July 2003 14:47:44 UTC

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