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Re: Terminology (was Re: article on URIs, is this material that can be used by the)

From: <noah_mendelsohn@us.ibm.com>
Date: Wed, 27 Jun 2007 16:52:19 -0400
To: Pat Hayes <phayes@ihmc.us>
Cc: Dan Brickley <danbri@danbri.org>, "Henry S. Thompson" <ht@inf.ed.ac.uk>, Pat Hayes <phayes@ihmc.us>, Tim Berners-Lee <timbl@w3.org>, www-tag@w3.org
Message-ID: <OF60639196.18CDDDAC-ON85257307.0070DD1A-85257307.00726DE1@lotus.com>

Pat Hayes wrote:

> >* Having HTTP GET indicate in the results of an interaction whether 
> >has been contacted is in fact an information resource, and thus whether
> >the representation stands in the sort of relationship to the 
> resource that
> >we expect for information resources (which >can< by definition be
> >faithfully sent in message), is useful.
> There I disagree. Your locution here reveals the essential point. 
> "the sort of relationship to the resource that we expect for 
> information resources". WRONG. In fact, I expect to have at least TWO 
> distinct relationships to information resources. I expect to be able 
> to access them, using some kind of xxxTP protocol, AND I expect to be 
> able to refer to them. Referring to them is exactly like referring to 
> anything else: the same relationship is involved, the same semantic 
> theories apply, and the same inference processes can be used for 
> referential languages. When referring, the nature of thing referred 
> to is almost irrelevant, in fact. The distinction between kinds of 
> resource matters only because non-information resources can't be 
> accessed.

Careful.  I didn't say that either the access or the reference stood in 
some relationship to the resource.  I said that for information resources 
on the Web in particular, we expect that >representations< stand in a 
certain relationship to the information resource being represented.  I 
agree that this is not currently defined with mathematical precision, but 
I think the gist is clear.  If the resource is the text of the U.S. 
Declaration of Independence, which consists of a sequence of paragraphs 
comprised of sentences comprised of words, then we generally expect a Web 
representation to convey that sequence or paragraphs/sentences/words.  It 
can do that in text/plain ASCII, in HTML, perhaps even in an image of the 
characters.  Because the Declaration is an information resource, we may 
aspire to having a representation convey its essence.  Were we to have 
instead the resource Mr. Thomas Jefferson (the person), then we would 
assume that any attempt at a representation would be somehow further 
removed from his essence, since he himself could not be sent through a 
wire, even when he was alive.  That was the point I was making.

You are correct that, somewhat independent of what I've just said about 
representations, the distinction between reference and access is imporant. 
 I think Dan is correct that the Web as deployed, and the Web Architecture 
Document (if read a bit sympathetically) provide for both. 

Here's what I think may be the essence of the confusion:  there are 
certain systems in which it is by definition possible to attempt to access 
anything that can be referenced.   The Web, at least when URLs are used 
for reference, is one such system.  Let's consider another.  In many 
computer architectures, memory locations are identified by pointers.  I 
can use those for reference.  For example, I can say: "Hey, Pat, I think 
that crash was due to a bad value in memory at location 0X12345".  I've 
made a reference, but no access.  I haven't gone to find the value in the 
memory, just talked (referenced) about it.  On the other hand, if I'm in 
the world of software running on that computer, >any pointer you give me I 
can try to access<.  That doesn't mean that reference and access are the 
same thing.  It doesn't even mean the access will always succeed;  I might 
get a protection exception.  Within the computer though, we posit that 
there is some uniform means (probably a LOAD instruction) that I can use 
to attempt to access any item for which I have a reference.

At the very least for http URIs, almost surely for all of what we used to 
call URLs, and arguably for all URIs, the Web is like this.  I can 
reference something by giving you a URI in this email.  For example, I can 
tell you that my employer's Web site is http://www.ibm.com.  That's a 
reference.  The Web has the interesting property that, pretty much 
independent of what http URI I give you, you can try to access it.  That 
doesn't mean we're confusing reference and access, but it does make clear 
a sense in which they come together.  That's what makes the Web so 
suitable for dynamic exploration.

Of course, there are many other environments in which this connection 
doesn't hold.  We can with some fidelity reference human beings by their 
names, but in most cases knowing my name doesn't guarantee you a strategy 
for finding (referencing) me.

BTW: I will mostly be off email for a couple of weeks.  If this little 
discussion continues, I'm unlikely to contribute much.


Noah Mendelsohn 
IBM Corporation
One Rogers Street
Cambridge, MA 02142
Received on Wednesday, 27 June 2007 20:52:02 UTC

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