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Re: null namespace Re: Next steps for the ARIA syntax discussion

From: <noah_mendelsohn@us.ibm.com>
Date: Fri, 23 May 2008 09:25:13 -0400
To: "Charles McCathieNevile" <chaals@opera.com>
Cc: "public-html@w3.org" <public-html@w3.org>, "public-xhtml2@w3.org" <public-xhtml2@w3.org>, "Robert J Burns" <rob@robburns.com>, "wai-xtech@w3.org" <wai-xtech@w3.org>, "www-tag@w3.org" <www-tag@w3.org>
Message-ID: <OF3EF271EA.79CA9216-ON85257451.006F8E73-85257452.00499E5F@lotus.com>

Charles McCathieNevile writes:

> The fact that the interpretation of the attribute depends on 
> its element is a way of dealing with collisions that can arise.

I don't think so.  As far as I know, the scoping of attributes to the 
elements on which they appear is a characteristic of XML itself, and was 
introduced before namespaces were invented.  You can "prove" this, because 
in XML, a DTD can give different defaults to attributes named "A" 
appearing on element "X" vs. attributes with the same name appearing on 
"Y".  So, the attribute declarations are scoped to the element.  I became 
active in the XML community after the namespaces recommendation was pretty 
much done, but I suspect that the formulation that the attributes need 
neither a prefix nor an associated (perhaps inherited or inferred) 
namespace for scoping is a reflection of the scoping characteristics of 
attributes in XML.

Also, and again others are more expert in the nuances, I believe that one 
refers to elements and attributes being "not in a namespace" as opposed to 
being "in the null namespace".   The reason, I believe, is that a 
namespace suggests a single managed "space" of names.  Usually the 
assignment of names in a namespace is coordinated by a single party, 
typically the "owner" of the namespace name URI, or by several parties 
cooperating.  Conversely, there are zillions of attributes and elements 
named "A" in XML documents of many different sorts.  Collisions among 
those tags is in general not intentional or coordinated.  In that sense 
there is no null namespace, just tags "not in a namespace".

Also, to support self-description on the Web, you can put up a RDDL or 
similar document "at" the namespace name URI.  This can enable some degree 
of automated processing of the markup (perhaps automated styling with an 
XSL stylesheet) even by user agents that have no built in "knowledge" of 
the namespace.  This clearly can't be done for names not in a namespace. 
The ability to support such self-description is among the reasons, I 
believe, that some members of the TAG find qualified names to be highly 

My purpose here is not to weigh in on the net pros or cons of aria-xxxx. 
Having worked for several years at Lotus, a company that sold software for 
use by millions of end users, I'm very, very sympathetic to the pressures 
on companies like Opera that are well along in preparing to ship code. 
Here I'm merely to discuss some of the issues relating to tags that are 
vs. are not in namespaces. 


Noah Mendelsohn 
IBM Corporation
One Rogers Street
Cambridge, MA 02142
Received on Friday, 23 May 2008 13:25:09 UTC

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