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 12:41:32 -0500
Message-Id: <p06001207bb41c7b4b5da@[]>
To: "Jonathan Borden" <jonathan@openhealth.org>
Cc: "Michael Day" <mikeday@yeslogic.com>, www-tag@w3.org

>Actually ...
>>  >  > Think about it: it that were true, then by writing "1404 West La Rua
>>  >>  St., Pensacola" you would have created a link to something that does
>>  >>  not exist, which is impossible.
>>  >
>>  ><a href="http://this.does.not.exist.com/index.html"> Link </a>
>>  >
>>  >Have I not just created a link to something that does not exist?
>You have created a link to a resource which may or may not return a
>representation on dereferencing the URI

OK, but that's my sense of 'link' and the more limited sense of 
'resource', what TimBL calls an information resource. I'm quite happy 
with that notion, of course, as long as we can agree to stick to it.

>... 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?

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.

>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?? 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.

>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*.

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.

>>  >A citation of a book giving page number, paragraph and line number is
>>  >still a link, even if the book no longer exists. Not all links can be
>>  >traversed or dereferenced.
>>  >
>>  >"Creating a link to" == referencing, in some cases quite optimistically
>>  Ah.  OK, with that usage, then I would agree; but that is a VERY
>>  strange usage of "link", at least to one reader.  And I think it is
>>  highly misleading, since "link" usually *does* imply at least the
>>  possibility of dereferencing, in principle, in an ideal world, etc.;
>>  whereas this sense of 'link' to simply mean 'refer to' clearly never
>>  has, and never had, any such implication.  (What a referring name
>>  enables you to do is to *think* and *talk* about something, not to
>>  actually get your hands on it.)
>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?

>I don't see the problem with: "create a
>link to" == reference.

Well, I agree, that is OK also, although it makes a lot of the TAG 
document wrong.  But what isn't OK is conflating the earlier sense 
with this sense, because they are completely different and have 
different properties.

>In any case the URI "urn:isbn:xxx" does allow you to reference a book, and
>using this URI you might be able to 'dereference' a physical copy of the
>book i.e. via an indirection service such as amazon.com

You might; but you also might not.  (Last year I tried to get hold of 
a book on modern Japanese prints, a present for someone. There are 
dozens of isbn#s for these books, but no copies for sale anywhere, 
not even on Ebay.) It has nothing to do with being a reference, 
though.  And almost certainly it is false to claim that there is a 
*single global* link from a URI to its corresponding resource in this 
sense, right? (The only example would be a case where there was just 
one copy of the book left in the entire world, in which case you 
almost certainly can't buy it on Amazon.)

>With this sense of 'link' it is
>>  clearly just a mistake to think that there must always be a unique
>>  thing 'linked to', for example: notoriously, one can refer to things
>>  that do not and never have existed, and one can, and often does,
>>  refer ambiguously.
>right an such resources (that never have physically existed) may indeed have
>representations e.g. a picture of a unicorn, or a written description.

Representations, yes: links to them (in any useful architectural sense), no.

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Received on Monday, 21 July 2003 13:41:35 UTC

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