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

Re: httpRange-14

From: Tim Berners-Lee <timbl@w3.org>
Date: Fri, 25 Jul 2003 16:14:07 -0400
Cc: Norman Walsh <Norman.Walsh@Sun.COM>, www-tag@w3.org
To: "Roy T. Fielding" <fielding@apache.org>
Message-Id: <8BDD9C4A-BEDC-11D7-9DFD-000393914268@w3.org>


On Friday, Jul 25, 2003, at 00:51 US/Eastern, Roy T. Fielding wrote:

>
>> It isn't illegal or illogical or wrong to use http URIs to identify
>> things that aren't documents. But it is potentially misleading, is
>> likely to introduce ambiguity that it would be better to avoid, and is
>> not obviously superior to mechanisms that don't have these defects.
>> (Or, more accurately, if it is superior, I don't see how.)
>>
>> Progress?
>
> No.

Huh? Yes, I hope. I really hope we can move forward on this.

> You have left out all of the HTTP-based services that are not
> documents, by any stretch of the imagination, and yet still are
> identified by "http" URIs.  "almost all" is not ALL.

You are of course right that there are services,
but those still are not people. Norm's argument stands.

You are formally right, but with respect to Norm's argument, you are 
splitting hairs.
If we call the things which are there for GET "documents"
and the things which are there for POST, "services",
and the things which are  just there for HEAD "hopefulls",
then all these classes of thing (of which we talk about documents
mostly, as Norm did in his simplification) are still not people.

If you take the union of all these things, it does not include people.

It is still important for somebody who visits Mark Baker's web page
to be able to make comments about it as a work without having
to call him to find out whether the URI is being used for him or
his dog or a galaxy somewhere.

>   I see no
> reason why the web architecture document should claim something
> that is obviously false, particularly when it is used within
> millions of transactions every day.

The arch document can elaborate the above classes,
which fixes that problem.
But this does not affect Norm's argument.

> The fact is that "most users" don't know that the target of a submit
> button is a URI that usually begins with "http".  It is also a fact
> that most users of automated tools based on libwww-perl never see
> the URI.  It is reasonable to expect the same will be true of WSA.
> If most users think that "http" means document, then all I can say
> is that most users are not developers of WWW technology.
>
> http URIs identify resources via the http naming convention.  That
> is all that ever needs to be said, anywhere, for any system that
> makes use of http URIs (semantic or otherwise).

I am sorry, while there are two distinct things which are meant
by a single URI (say, Mark and his web page), then the system
is unusable for semantic web purposes until we can resolve which is 
used.

[...]
| In any case, making claims about resources by examining their
> scheme completely fails when considering all of the other schemes,
> especially "urn".

Nonsense.
The mailto: URIs denote endpoints in a store and forward 
message-passing system
called email.  The operations which can be performed are primarily to 
mail to them using SMTP, hence the name "mailto".  They also appear in 
the protocol in other ways.
That was the intent of the Web design, and it remains it from my point 
of view.

They do not support GET, and I know you can say that you can make a 
gateway to them dreaming up something which is for you a representation 
of them, and I can too, but that is a kludge.  It doe not render a 
representation of an information resource, it tells you what some 
program knows about messages sent  to and from or the owner of the 
mailbox. Useful, but not a GET of the mailbox.  (Folks, we are talking 
SMTP, not IMAP here!  Not a random access retrieval protocol, ot a 
space of accessible information objects, but a posting and forwarding 
system)

It is really usful ht we know that ISBNs apply to books, ISSNs to 
magazines, SSNs to people, vehicle license number to vehicle licenses.

It is also really important in the architecture to be able to declare 
new different types of conceptual object and make a new subspace of the 
URI space for them to be.

> There are no special categories of "information resource".

You say no, I say yes.
For me an information resource is an important concept.
For me that is what the information space which is the (HTTP GET) web 
is made of.
IT seemed, independently, quite clear to Pat too - in fact, he was 
appalled and confused by the arch doc's lack of distinction of the 
concept.

> Any URI
> provided within a retrieval context is assumed to be an information
> resource.

The architecture is *not* one in which the classes are deduced from 
context.

>   The scheme is irrelevant to such assumptions.  The right
> solution is to fix the Semantic Web so that it doesn't throw away
> method semantics, as it does currently by assuming a URI denotes
> what is obtained by a response to GET.

It does NOT assume that it denotes what you get in response.
Please don't put words in people's mouths, incorrect ones.
This is explained in painstaking detail in
http://www.w3.org/DesignIssues/HTTP-URI.html,
  which was presented at the TAG F2F in vancouver in 2002-09.

It denotes the abstract information resource.
To repeat this well-worn thread, why do we say that the URI identifies
something with information content about a car, rather than the car? 
Because
the general expectation upon which the working of the web in practice 
relies
is that the information content will be more or less in some way the 
same when a URI is dereferenced twice.  We want roughly the same 
picture, not anything about roughly the same car.  The concept of 
identity has to do with what is invariant about the measurable 
qualities of something, and in this case they are the information 
content, not the subject.   I use "representation" to relate the (meta 
data and bits) to the picture, you use it to relate the (metadata and 
bits) to the car which is the subject of the picture.  The concept of 
an "information resource" is well defined in terms of the conveying of 
information, and we need tit to be able to talk about equivalent and 
translated representations, etc. The concept of the subject of the 
picture is very weak, as for most pictures and many many web pages  it 
is not well defined, and also it is not necessary. When someone posts 
the poem "Khubla Khan" on a web site, the poem is the information 
resource, not Khubla Khan. If you had to chose a subject for the page 
to be the tings "represented" a la Roy and Mark, then would it be 
Khubla Khan, or the pleasure domes, or maybe Alph the sacred river ... 
in your design, Roy no one knows what is being represented, no one 
knows what the URI stands for.   In my design, the URI means the poem, 
and that works.

Tim
>
> ....Roy
Received on Friday, 25 July 2003 16:14:01 UTC

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