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Re: Are QNames in Attribute Values Permitted as Identifiers?

From: <noah_mendelsohn@us.ibm.com>
Date: Mon, 22 Apr 2002 17:45:17 -0400
To: reagle@w3.org
Cc: bobatk@microsoft.com, ian@w3.org, w3c-ietf-xmldsig@w3.org, www-tag@w3.org, xml-dist-app@w3.org
Message-ID: <OF7BEB6C67.4F8546D1-ON85256BA3.0077F967@lotus.com>

SOAP adopts the QName type for many purposes, but generally depends on the
value space, not the lexical space as being semantically interesting.  From
[2]  (your reference):

"The ·value space· of QName is the set of tuples {namespace name, local
part}, where namespace name is an anyURI and local part is an NCName. The
·lexical space· of QName is the set of strings that ·match· the QName
production of [Namespaces in XML]."

So, the values of Qnames are indeed expanded names.  In reviewing the
latest SOAP editors drafts, I think this is a point that could be made more
crisply (I'm cc:'ing distApp).

Still, use of QName can be taken to imply the "expanded name", as that is
the value space of QName.  Of course, the lexical space uses prefixing, so
use of the lexical space may depend on having a proper definition for the
prefix in scope.

Noah Mendelsohn                              Voice: 1-617-693-4036
IBM Corporation                                Fax: 1-617-693-8676
One Rogers Street
Cambridge, MA 02142

                      Joseph Reagle                                                                                                     
                      <reagle@w3.org>          To:       ian@w3.org, www-tag@w3.org                                                     
                      Sent by:                 cc:       bobatk@microsoft.com, w3c-ietf-xmldsig@w3.org, www-xkms@w3.org, (bcc: Noah     
                      www-tag-request@w         Mendelsohn/Cambridge/IBM)                                                               
                      3.org                    Subject:  Are QNames in Attribute Values Permitted as Identifiers?                       
                      04/19/2002 11:26                                                                                                  
                      Please respond to                                                                                                 

I'm noting that QNames are increasingly being used as identifiers within
specifications. For example, XKMS is moving this way given the precedence
set by SOAP, I'm seeing it in other ws-security work as well.

My primary question is an architectural one: are these acceptable
replacements for URIs as identifiers within our specifications? (They're
certainly easier to read!) What is the identifier, the string "foo:bar" or
the tuple [0]? Do we expect all specs to treat them uniformly in the next
version of XML? What about present versions?

My second question is an unfounded question about security implications. I
haven't thought it through, but I wonder if there's any security
ambiguities arising from the use of QNames as identifiers within an
attribute value. When you sign a document via XML Canonicalization, it's
attribute value is a string-value (not an "expanded-name" in XPath
terminology, nor a QNAME in others'), but it also doesn't rewrite prefixes
either so I feel safe. UDDI's schema-centric c14n [1] does rewrite
namespace prefixes [2], but it's also schema centric -- I'm not sure what
the result is there. (Bob?) And in other applications, where both sorts of
processing might be done (attributes as strings versus QNAMEs) it's hard to


[0] http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/#QName
[1] http://www.uddi.org/pubs/SchemaCentricCanonicalization-20020213.htm
[2] http://lists.w3.org/Archives/Public/w3c-ietf-xmldsig/2002JanMar/0204
Received on Monday, 22 April 2002 18:01:28 UTC

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