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Re: Revisiting namespaceDocument-8

From: Norman Walsh <Norman.Walsh@Sun.COM>
Date: Fri, 13 Jan 2006 14:52:00 -0500
To: www-tag@w3.org
Message-ID: <8764onrjmn.fsf@nwalsh.com>
[ The TAG has made progress since this message was originally posted,
  but I have had a long-standing action item to reply to it. ]

/ noah_mendelsohn@us.ibm.com was heard to say:
| Norm:  Overall, this seems like a good direction.

Thanks :-)

| That said, one aspect of the namespace issue has been on my mind since we 
| "resolved" httpRange-14.  The paraphrase of that resolution is: "an 
| information resource can return HTTP 200 and representations; a non-info 
| resource should redirect, typically using 303".  So far so good.  If I 
| write a poem, I can give it an HTTP URI and serve up representations;  if 
| I want to give the poet himself an HTTP URI, then that must redirect using 
| 303 to a resource that is descriptive of the poet.

Or use a URI with a fragment identifier so that the URI of the
document and the URI of the poet are distinct. But I take your point.

| Now the questions about namespaces:  is a namespace an information 
| resource and therefore the sort of thing that can respond with a 200? 
| Certainly it's abstract in a way that the poet is not.  It has no mass and 
| won't knock you over if you run into it.   Web Arch characterizes an 
| information resource as  one for which  "all of their essential 
| characteristics can be conveyed in a message"[1] What are the essential 
| characteristics of a namespace, and can they be completely conveyed? 

As near as I can tell, a namespace is an intellectual construct that
can't possibly have any substance other than information. I'm no
philosopher, but I'm comfortable with the statement that a namespace
is an information resource.

| I note that seem to be abstractions that are not clearly information in 
| the Web arch sense.  Consider the concept of the "color red".  I might 
| want to make an rdf statement:
|
|         :noah :likes <http://examples.org/colors/red>
|
| Can the essential characteristics of a color be conveyed in a message. 
| Does our httpRange-14 resolution allow a 200 status for 
| http://examples.org/colors/red?  If not, is a namespace this sort of 
| amorphous abstraction, or is it more specifically a collection of 
| information, presumably including at least the collection of names 
| qualified by a given URI?

There are intellectual constructs, like beauty, that have an
ineffeable quality. I don't know if "red" is ineffable or not. Quite
possibly, I think.

But I don't think namespaces fall into that category. I don't think
all abstracts are by nature ineffable.

| If we take the narrow interpretation that the namespace is in fact just 
| the set of qualified names, then it's not clear that the representations 
| we're proposing to return are in fact representations of the namespace. 

How so? If a namespace is just a set of qualified names then it would
seem to me that any document which enumerates the list of names (e.g.
http://www.w3.org/2005/xpath-functions/) is manifestly a
representation of the namespace. If it gives additional information
(like pointers to schemas and stylesheets), that's a good thing. If it
gives less information (e.g., pointers to schemas and stylesheets but
w/o enumerating or describing the terms in the namespace), that may be
a low quality representation, but we're not responsible for the
quality of representations.

| They seem to be representations of a resource that is a description of the 
| namespace.  Isn't it exactly that distinction that caused us to argue for 
| a 303 in the case of the poet?

It doesn't seem that way to me. As I said, I can't think of anything
about a namespace that I couldn't communicate with a representation.
The same isn't true of physical constructs like the poet or ineffable
concepts.

| As a practical matter, users are going to 
| be quite annoyed if we require that for every namespace they deploy a 
| server that uses a 303 redirect to get you to the RDDL, but I'm curious 
| what our theoretical justification is for allowing a 200 from the 
| namespace name. 

I hope I've explained why I think it's justified.

| Obviously, the last thing I'd advocate is a full reopening of 
| httpRange-14, but I do think it's worth convincing ourselves that the 
| resolution we've adopted can be applied consistently and conveniently to 
| the important case of namespaces and their descriptions.   If we stick 
| with our resolution of httpRange-14, then I think we need to be prepared 
| to set out what the information is that "comprises a namespace", so that 
| we can show that it can be "conveyed", or else we need to suggest use of 
| two URI's and a 303 for each namespace.

I don't think we need to do that. Users won't, even if we said they
should, so I think it would be best if we agreed that it wasn't
necessary :-)

                                        Be seeing you,
                                          norm

-- 
Norman.Walsh@Sun.COM / XML Standards Architect / Sun Microsystems, Inc.
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Received on Friday, 13 January 2006 19:52:16 UTC

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