Re: URI documents

Harald Tveit Alvestrand wrote:
> 
> At 16:06 24.12.97 -0800, Larry Masinter wrote:
> >Between:
> >
> >a) Roy's last URL syntax draft what we did a last call on.
> >b) Roy's attempt to turn this into a URI document, at (I believe
> >   the original suggestion of the area directors) by doing
> >   a global substitute
> >c) Leslie's attempt to split (b) into a URI and a URL document
> >d) Larry's attempt to create a single document which discusses
> >    URIs and URLs.
> >   (ftp://ftp.parc.xerox.com/pub/masinter/uri-url-syntax.txt)
> >
> >We have heard from a few folks, but not a lot. To recap:
[...]
> To me in my AD position, the parameters of a solution are:
> 
> - The solution must document the overall concept that embraces all the
>   identifiers of this class, commonly called "URI". (This rules out a)
> - The solution must not invalidate current UR* schemes, including URNs.
> - The solution should not needlessly complicate or constrain future UR*
>   schemes
> 
> All I can say is - I hope we find a solution.

Harald, it would help me out if you would
please point out how it is that (b) is not a solution.
I read it quite carefully and I find it satisfactory.

I don't understand the arguments from the folks who
find it unsatisfactory; rather, I think I understand them,
but I can't find any technical content to them. They
seem to boil down to "but we're not sure it's going to
work that way for URNs."

I am trying to find (c) to review it, but I'm not having
any luck.


Since Larry asked, I'll (re-)state the W3C opinion: we're
heavily invested in the notion of a single, extensible universal
address space:

============
Univeral Resource Identifiers -- Axioms of Web architecture
Tim Berners-Lee
Date: December 19, 1996 
[1]http://www.w3.org/DesignIssues/Axioms.html

Universal Resource Identifiers

The Web is a universal information space. It is a space in
the sense that things in it have an address. The
"addresses", "names", or as we call them here identifiers,
are the subject of this article.  They are called Univeral
Resource Identifiers (URIs). 

On object is "on the web" if it has a URI.  Objects which
have URIs are sometimes known as "First Class Objects"
(FCOs).  The Web works best when anything of value and
identify is a first class object.  If someothing does not have
a URI, you can't refer to it, and the power of the Web is the
less for that. 

By Universal I mean that ...
============

The name has changed over the years (from UDI=Universal Document
Identifier to URI=Universal Resource Identifer to
URI=Uniform Resource Identifier) but the concept remains
the same. Not to mention the fact that the gizmos themselves
remain the same (try
http://info.cern.ch/hypertext/WWW/TheProject.html and you'll
still get information about the World Wide Web project at CERN.)

So we (W3C) disagree with what Leslie wrote:

Leslie, 23 Dec 1997:
>Roy, 22 Dec 1997:
>> Within the WWW, a fragment serves the purpose of a client-side
>> specialization of the resource identification.  It is implicit that
>
>URIs are not limited to the WWW (okay, these are getting into old
>arguments...).

URIs are limited to the WWW by definition; that is, the
WWW is the set of things addressable by URIs.

I have asked whether folks
expect URNs to fit into the same protocol/software slots
as today's URIs do (e.g. in proxied HTTP GET requests,
Java URLConnection() parameters, libwww URI parsing
calls, etc.) but I don't think I got a clear answer. If
URNs _are_ expected to fit into those slots, then
we need a spec for those slots, and (b) is good enough for me.
(we also need one registry of schemes, and one
process document for adding items to that registry). If
URNs are _not_ expected to fit in those slots, then
I have a problem with that.

The axioms document[1] goes on to say things like:

=============
Axiom 1: Global uniqueness 

 It doesn't matter to whom or where you specify that URI, it
 will have the same meaning.
=============

These axioms are exactly that: arbitrary assertions without
supporting evidence. They take on value as folks choose
to accept them (folks being implementors, information providers,
etc.) "The value of
a network goes up as the square of the number of connected
resources" and all that.

So while it's perfectly possible
to use names/addresses/identifiers that aren't part of
the URI space, any such set of names doesn't benefit from
the value of being part of the URI space. At W3C, we
think there's plenty of ways to improve the operation of
the URI space, and no reason to invest in something
that doesn't interoperate, at this point.



=============
Axiom 3: non unique 

 URI space does not have to be the only universal space


The assertion that the space of URIs is a universal space
sometimes encounters opposition from those who feel
there should not be one universal space. These people
need not oppose the concept because it is not of a single
universal space: Indeed, the fact that URIs form universal
space does not prevent anyone else from forming their own
universal space, which of course by definition would be
able to envelop within it as a subset the universal URI
space. Therefore the web meets the "independent design"
test, that if a similar system had been concurrently and
independently invented elsewhere, in such a way that the
arbitrary design decisions were made differently, when
they met later, the two systems could be made to
interoperate. 

There may be in the world many universal spaces, and
there need not be any particular quarrel about one
particular one having a special status. (Of course, having
very many may not be very useful, and in the World Wide
Web, the URI space plays a special role by being the
universal space chosen in that design.) 

For example, it would be possible to map all international
telephone numbers into URI space very easily, by inventing
a new URI "phone:" after which was the phone number. It
would in fact also conversely be possible to map URIs into
international phone numbers by allocating a special phone
number not used by anyone else, perhaps a special
country code for URI space, and then converting all URIs
into a decimal representation. In that case, both URIs and
phone numbers would be universal spaces. Identifiers in
one space would be consisting only of numbers, and in the
other of alphanumeric characters. One would be shorter
than the other, but there is no reason why, in principle, the
two could not co-exist, allowing you to dial any Web object
from a telephone as a telephone number, and point to any
phone from a hypertext document.

So, on this last axiom rests not specifically the operation of
the web, but its acceptance as a non-domineering
technology, and therefore our trust in its future evolvability.
=============

-- 
Dan Connolly, W3C Architecture Domain Lead
http://www.w3.org/Architecture/

Received on Friday, 2 January 1998 10:27:03 UTC