W3C home > Mailing lists > Public > xml-uri@w3.org > May 2000

Empty URIs

From: Tim Berners-Lee <timbl@w3.org>
Date: Wed, 17 May 2000 20:01:11 -0400
Message-ID: <00e101bfc093$4e26bbb0$b0ec5c8b@ridge.w3.org>
To: <xml-uri@w3.org>, "Eve L. Maler" <Eve.Maler@east.sun.com>

-----Original Message-----
From: Eve L. Maler <Eve.Maler@east.sun.com>
To: xml-uri@w3.org <xml-uri@w3.org>
Date: Wednesday, May 17, 2000 11:50 AM
Subject: Re: Are *relative* URIs as namespace nemes considered harmful?


>At 05:53 PM 5/16/00 -0400, Tim Berners-Lee wrote:
>>One example, given by Chris Lilley I think, from WebCGM experience, is
that
>>of a schema which defines a language and sees it in the same document in a
>>deliberately (not accidentally) self-referential way.  [The C program
module
>>parallel would be a program file which defines a number of functions, and
>>makes calls  to those functions within the same file which defines them.]
>>For example, the schema for schemas could bootstrap itself into existence
>>referring to itself as "#".
>
>If I understand correctly, you're suggesting that the namespace URI is
>self-referencing (assuming you actually plan to dereference something) by
>virtue of being empty.  However, note that such a value is an empty URI
>reference [1], not a relative URI reference; normal base resolution does
>not apply because the referent is always the current document.


Well, actually it wasn't empty there exactly because as you point out the
spec
[brokenly IMHO]  assigns a special meaning (of which I don't understand the
purpose) to
an empty URI. An empty URI is defined by the URI RFC to refer to
the current document.  Chris had to use "#" to refer to the current document
for this reason. But I wasn't going to get into that discussion then... but
I suppose a thread for it would be appropriate.

>We've been focusing on only one case (relative URIs) to the exclusion of
>another important one (empty URIs), and there may be tricky corners to the
>latter because the Namespaces spec defines special features for empty
>strings as namespace declaration values.  (I think the presence of the bare
>"#" in your example above negates its use as an "unsetting" declaration...)


That is indeed why it was there.
Tim BL

>         Eve
>
>[1] http://www.ietf.org/rfc/rfc2396.txt, Section 4.2
>--
>Eve Maler                                    +1 781 442 3190
>Sun Microsystems XML Technology Center    elm @ east.sun.com
>
Received on Thursday, 18 May 2000 02:33:49 UTC

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