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Two questions about URIs

From: Pat Hayes <phayes@ai.uwf.edu>
Date: Tue, 16 Oct 2001 12:10:47 -0500
Message-Id: <p05101028b7f212af39a6@[]>
To: uri@w3.org
I have a couple of questions about URIs that may have already been 
discussed or even answered. If so, please point me at the archive; 
but if not, they ought to be.

The first is about URIs as names. Given the contemporary unified 
understanding of URI's, I gather that it is appropriate to generally 
consider any URI to be a name, by which I mean an expression which is 
understood to refer to something; or, as logicians say, to denote it. 
Exactly what a name refers to, and how one can determine what it 
refers to, are complex questions that might require complex answers, 
but I want to focus on just one issue that seems to be special to 
URIs and not arise in other naming schemes (so acutely, in any case.)

Although the term 'URL' is now deprecated, the fact remains that the 
vast majority of URIs in actual use start with http: , https:, or 
ftp:, and are used primarily as a kind of global file-address. That 
is, they are used by communication protocols to identify a global 
address on a computer network where some data can be accessed. This 
is the basic traffic of the Web. Now, my question is: is there 
supposed to be any particular relationship between the referent of 
such a URI, considered as a name, and the file that it locates in the 
global file network? For example, should we say that a URI beginning 
with http: must *denote* or *refer to* the file itself, or to the 
web-page image on a screen produced when that file is accessed by a 
browser (ie the hypertext, rather than the markup that 'describes' 
it), or perhaps to some other thing that is itself named (in some 
sense) by that hypertext? Or is there some other kind of relationship 
that should be assumed between the referent and the file? (What?) Or 
can the referent of such a URI be assigned freely, with no reference 
to the file that it 'points to' in its role as a locator?

My second question concerns some rather opaque wording in RFC 2396, 
section 1.1, under 'resource', which reads:
         The resource is the conceptual mapping to an entity or set of
          entities, not necessarily the entity which corresponds to that
          mapping at any particular instance in time.  Thus, a resource
          can remain constant even when its content---the entities to
          which it currently corresponds---changes over time, provided
          that the conceptual mapping is not changed in the process.

This seems to imply a three-way distinction with two mappings, rather 
than the simple two-way name/entity distinction suggested by the term 
'resource identifier'. A URI identifies (denotes?) a resource, which 
in turn has some *content* (the entities to which it currently 

URI ----(identifies)---->resource-----(corresponds to)----->entity

Apparently the identification mapping is fixed, but the 
correspondence mapping can change with time.  Is this a fair 
understanding of this text? If so, the entire notion of a URI simply 
denoting or naming something seems to need re-thinking.

I request clarification of what this is supposed to mean, with 
particular reference to the intended distinction between 'resource' 
and 'entity', and between 'identifies' and 'corresponds to'.

Pat Hayes

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Received on Tuesday, 16 October 2001 13:10:45 UTC

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