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

Re: Empty URIs

From: Eve L. Maler <Eve.Maler@east.sun.com>
Date: Thu, 18 May 2000 10:28:12 -0400
Message-Id: <4.3.1.2.20000518102159.00ae55c0@abnaki.East.Sun.Com>
To: <xml-uri@w3.org>
At 08:01 PM 5/17/00 -0400, Tim Berners-Lee wrote:
> >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

My main point, though, was that RFC 2396 defines "empty URI" differently 
from "relative URI", and also defines its "absolutization" differently.  If 
you have xmlns="#", then the URI portion of this URI reference is still 
empty, and if you intend to use it for any retrieval, or if the ultimate 
decision is to compare after absolutization, then it needs to be 
absolutized too.  Any solution needs to take into account the use cases of 
"" (with its special Namespaces meaning), "#", and "#foo".

Since a base URI isn't used in this case, it seems to me there is no 
canonical absolute form provided by the document itself, which could easily 
lead to false positives in absolutized comparison.

         Eve
--
Eve Maler                                    +1 781 442 3190
Sun Microsystems XML Technology Center    elm @ east.sun.com
Received on Thursday, 18 May 2000 10:28:00 UTC

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