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Re: Are *relative* URIs as namespace nemes considered harmful?

From: Liam Quin <liam@holoweb.net>
Date: Wed, 24 May 2000 14:01:44 -0400
To: xml-uri@w3.org
Message-ID: <20000524140143.C60567@dirk.holoweb.net>
On Wed, May 24, 2000 at 01:41:52AM -0400, Tim Berners-Lee wrote:
> From: Liam Quin <liam@holoweb.net>
>>URLs (specifically) do not guarantee that they will return teh
>>same octet stream when accessed each time. Many do not, in fact.
> 
> I diasagree with you here.  It is true that the URL *technology* does not
> (unlike md5:) guarantee you the same thing each time, BUT
> the HTTP spec determnes that if you get 200 OK back from
> a GET for a URI then the server returns you a representation of the
> (abstract) resource identifid by the URI.
Right, sorry if I wasn't clear.  I was not trying to criticise URLs,
but rather to show a difference between, for example, URLs in
practice and SGML public identifiers in theory.

Public identifiers are trying to solve a different problem than URLs --
once a text has been given a public identifer, you always get the same
text stream by dereferencing (in an unspecified way) a public identifier.

Public identifiers have the semantics we need for namespaces, and had
namespaces been designed in the SGML world, there's no doubt in my
mind that they would have been used for the purpose.

Either (1) the URI should be dereferencable, or (2) it must always
be given in the exact (possibly absolute) form expected by applications.
In case (1), dereferencing the URI to get the mapping adds an extra
layer of indirection, but adds expressive power and solves the conflict
between the specifications.

I still feel that the other end of a namespace URI should be a
(usually short) document that lists absolute and known identifiers for
the namespaces that are being used.  Such a document could itself use
namespaces, giving for the first time a way to combine two namespaces.

Lee

-- 
Liam Quin - Barefoot in Toronto - liam@holoweb.net - http://www.holoweb.net/
Ankh on irc.sorcery.net http://valinor.sorcery.net/
Co-author, The XML Specification Guide, Wiley, 1999
Forthcoming: The Open Source XML Database Toolkit
Received on Wednesday, 24 May 2000 14:01:45 UTC

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