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RE: Determining attribute uniqueness seems to require namespace prefix in Infoset

From: John Boyer <jboyer@PureEdge.com>
Date: Fri, 11 Aug 2000 17:13:09 -0700
To: "Donald E. Eastlake 3rd" <dee3@torque.pothole.com>, "Joseph Reagle" <reagle@w3.org>
Cc: <xml-names-editor@w3.org>, <www-xml-infoset-comments@w3.org>, "XML DSig" <w3c-ietf-xmldsig@w3.org>
Message-ID: <BFEDKCINEPLBDLODCODKEEFCCEAA.jboyer@PureEdge.com>
Hi Don,

I see where you are coming from now, and it is both interesting and correct,
but it means we need to be saying something more in DSig, if not in XML
Names.

The appendix refers to the attributes as 'unqualified'.  The section is not
saying that unqualified attributes are qualified by per element partitions
(because then it wouldn't be unqualified).  Instead, because it is
non-normative, it is saying that one is free to look at it this way if it
makes one feel better.

The implication is that "per element partitions" don't really exist and need
not be supported by conforming applications.  In other words, the material
on per element partitions is a convoluted way of saying that the only thing
which matters is that an attribute appears within an element and should
therefore be processed as though it were in that element's namespace unless
it has a non-empty namespace other than the element's.  As well, I think
this is what you are saying.

Unfortunately, it actually does matter quite a bit.  For starters, suppose
you have an HTML anchor with two hrefs, one unqualified and the other in the
HTML namespace.  Which does one use?  Put in another more general way, given
element E in namespace N, if one wants to obtain attribute A from E, which
of the following processing models is correct?

1) Attr = (N:E).get(N, A)
2) if Attr is null, Attr = (N:E).get("", A)

or

1) Attr = (N:E).get("", A)
2) if Attr is null, Attr = (N:E).get(N, A)

It makes a difference if the XML is <N:E xmlns:N="N" A="2" N:A="1">.  The
first model gives the attribute whose value is 1, and the second model gives
the attribute whose value is 2.

I don't think this can be explained away as a simple differing viewpoint
because I don't agree that all applications process attributes solely within
the context of the parent element.  The prime example of this is XSLT, which
uses XPath for template matching.

Lets compare the following four occurences of an element E by considering
the xsl-template's XPath expression that must match E based on whether the
value of an attribute A is 'test':

1) <N1:E xmlns:N1="http://www.w3.org" xmlns:N2="http://www.PureEdge.com"
A="test"/>
2) <N1:E xmlns:N1="http://www.w3.org" xmlns:N2="http://www.PureEdge.com"
N2:A="test"/>
3) <N1:E xmlns:N1="http://www.w3.org" xmlns:N2="http://www.PureEdge.com"
N1:A="Yikes" N2:A="test"/>
4) <N1:E xmlns:N1="http://www.w3.org" A="test" N1:A="Yikes"/>

The xsl-template cannot simply try to match on the local name A or else
element E in #2 would be matched, which is clearly not intended. If we add
to the XPath test a call to namespace-uri() to match the URI for N1, then #3
works but #1 doesn't.  If we add a test that finds the local name of A and a
namespace-uri() that is either blank or equal to the URI for N1, then #1 -
#3 work as expected, but #4 has two attributes that match the test.

If the claim is true that attributes should be processed within the context
of the parent, then A="test" would indicate that the xsl-template should
match N1:E in #4.  However, N1:A is clearly the attribute A in element E's
namespace, so for the purposes of the primary processing application for the
N1 namespace, N1:A and A are duplicates.

Personally, I don't believe in duplicate attributes.  The normative part of
XML Names makes it clear that the attributes are not duplicates in name
(which is a well-formedness requirement of XML), but if the non-normative
part of the spec invents some concept that makes the two attributes equal
for the purposes of processing, then a precedence must be specified. Which
one has precedence?  Until we know this, the proper xsl-template cannot be
written.

If I had to guess on a processing precedence, I would guess that the
namespace qualified version should take precedence.  Here's why:

I've been sitting here trying to figure out why the default namespace does
not apply to attributes, and the only thing that I can think of is that
unqualified attributes can then be used to apply an attribute value across
all namespaces.  In other words, a sort of default value to be used when no
namespace specific attribute is given. Consider the following bit of XML:

<E xmlns:N1="http://www.w3.org" xmlns:N2="http://www.PureEdge.com"
A="default" N1:A="Value for App that processes N1" N2:A="Value for App that
processes N2"/>

The information in element E can be used by one application that conforms to
specification given at the URI for N1, or it could be processed by a second
application that conforms to specifications given at N2, or it could be
processed by some other generic XML processing application.  If, by
convention, namespace qualified attributes took precedence over unqualified
attributes for processing, then the value for A would be
application-dependent.  If unqualified attributes took precedence, then A
would always equal default.

Perhaps XML names will not be changed or clarified, and perhaps they will
make no recommendation, but for a particular application, esp. a security
conscious one such as DSig, we should be saying what we expect our
processors to do when there are qualified and unqualified attributes with
matching local names.

John Boyer
Development Team Leader,
Distributed Processing and XML
PureEdge Solutions Inc.
Creating Binding E-Commerce
v: 250-479-8334, ext. 143  f: 250-479-3772
1-888-517-2675   http://www.PureEdge.com <http://www.pureedge.com/>



-----Original Message-----
From: w3c-ietf-xmldsig-request@w3.org
[mailto:w3c-ietf-xmldsig-request@w3.org]On Behalf Of Donald E. Eastlake
3rd
Sent: Friday, August 11, 2000 1:57 PM
To: John Boyer
Cc: xml-names-editor@w3.org; www-xml-infoset-comments@w3.org; XML DSig
Subject: Re: Determining attribute uniqueness seems to require namespace
prefix in Infoset



From:  "John Boyer" <jboyer@PureEdge.com>
To:  "Donald E. Eastlake 3rd" <dee3@torque.pothole.com>
Cc:  <xml-names-editor@w3.org>, <www-xml-infoset-comments@w3.org>,
            "XML DSig" <w3c-ietf-xmldsig@w3.org>
Date:  Fri, 11 Aug 2000 13:01:46 -0700
Message-ID:  <BFEDKCINEPLBDLODCODKMEEPCEAA.jboyer@PureEdge.com>
In-Reply-To:  <200008111839.OAA06618@torque.pothole.com>

>Hi Don,
>
>I did not mean to misquote you.  However, I haven't seen any W3C documents,
>nor implementations based on them, that use the term 'qualify' as you are
>using it.  It is not possible to 'qualify' an attribute with anything but a
>namespace URI.

It is syntactically not possible to attach any type of qulifying text
string to an attribute other than a prefix which corresonds to a URI.
However all non-prefixed attributes are automatically 'qualified' by
their element.

>In other words, in the example
>
><x xmlns:n1="http://www.w3.org" xmlns="http://www.w3.org" >
>  <good a="1"     n1:a="2" />
></x>
>
>There does not seem to be any basis in W3C work for the interpretation
>
>1) that 'a' is qualified as (n1:good):a,
>2) that 'a' is not qualified by a URI, and
>3) that 'a' is qualified by elements, including any URI which may qualify
>that element

See <http://www.w3.org/TR/1999/REC-xml-names-19990114> section A.2.  I
had to read this section and related material many times to make sense
out of them.

The unprefixed "a" above is in the Per-Element-Type Partition
associated with the element "good" in the namespace http://www.w3.org.
Whether you consider "a" to be "qualified" by n1:good or "local" to it
or part of it's Per-Element-Type Partition is all the same.  And it is
different from n1:a which is in the Global Attribute Partition.

>Therefore, when you said that the attributes "are qualified by their
>element", I assumed you meant 'qualify' in the sense defined by XML Names
>[1, see the abstract], which associates elements and attributes with a
>namespace identified by URI.  With this version of 'qualify', what you said
>is equal to what I said you said.

Unprefixed attributes are not associated with just a namespace.  They
are associated with an element which is in turn associated with a
namespace.

>Finally, ending most of our debate about this issue, Tim Bray states, "An
>attribute whose name contains no prefix is not in any namespace".  This
>means that in the first example of Section 5.2 of XML Names, the href in
<a>
>is not in the HTML namespace.

Well, it's not "directly" in any namespace.  It's in the
Per-Element-Type Partition of the element "a" in the HTML namespace.

No doubt debate is ended by a correct understanding of what Tim Bray
has said just as it is ended by a correct understanding of
http://www.w3.org/TR/1999/REC-xml-names-19990114 or a correct
understanding of the "Namespace Myths Exploded" material at xml.com.
The question is, what is "correct" understanding?

>This means if I put an HTML island in the middle of some XML by adding
>xmlns="http://www.w3.org/TR/REC-html40" to the html tag, then when I want
>the href of some anchor, I cannot simply say
>'get("http://www.w3.org/TR/REC-html40", href)'.  I must instead say
>
>1) get("http://www.w3.org/TR/REC-html40", href)
>2) if that fails, then get("", href)
>
>Once again... Yikes!

I'm not sure I understand this part of what you are saying but if your
understanding is that the treatment of unprefixed attributes is
fundamentally broken perhaps your understanding is incorrect.

Note that the Myths Exploded text keeps saying fuzzy handwaving things
like it doesn't really make much difference (which is why Appendix A
to the Namespaces document is not normative) because real applications
only handle non-prefixed attributes within the conext of the element
where they appear anyway.  In my mind it is just a difference in point
of view whether you consider such attributes to have no "qualifying
stuff" but to be used/operated on by their element, or you try to
induce a universal uniqueness by consdering them qualified by their
element name local part and their element's namespace if any.

>John Boyer
>Development Team Leader,
>Distributed Processing and XML
>PureEdge Solutions Inc.
>Creating Binding E-Commerce
>v: 250-479-8334, ext. 143  f: 250-479-3772
>1-888-517-2675   http://www.PureEdge.com <http://www.pureedge.com/>

Thanks,
Donald

>-----Original Message-----
>From: w3c-ietf-xmldsig-request@w3.org
>[mailto:w3c-ietf-xmldsig-request@w3.org]On Behalf Of Donald E. Eastlake
>3rd
>Sent: Friday, August 11, 2000 11:39 AM
>To: John Boyer
>Cc: xml-names-editor@w3.org; www-xml-infoset-comments@w3.org; XML DSig
>Subject: Re: Determining attribute uniqueness seems to require namespace
>prefix in Infoset
>
>
>
>From:  "John Boyer" <jboyer@PureEdge.com>
>To:  <xml-names-editor@w3.org>
>Cc:  <www-xml-infoset-comments@w3.org>, "XML DSig"
<w3c-ietf-xmldsig@w3.org>
>Date:  Fri, 11 Aug 2000 10:15:32 -0700
>Message-ID:  <BFEDKCINEPLBDLODCODKOEEKCEAA.jboyer@PureEdge.com>
>
>>Dear Editors,
>>
>>Please see the first example of Section 5.2 and the sentence immediately
>>above it, which says "Note that default namespaces do not apply directly
to
>>attributes" [1].  One chairman of the XML DSig group recently commented
>that
>>the word 'directly' may be intended to indicate that unqualified
attributes
>>inherit their namespace setting from the parent element.  This seems
>>sensible to me as the href attribute should be in the same namespace as
the
>>parent element <a>.
>
>No, I did not say that attributes "inherit their namespace setting
>from the parent element".  I said that they are qualified by their
>element.  That is, in
>
><b:a xmlns:b="foo:bar" c="xyz">
>
>it is "as if" c were actually b:a:c except, of course, that this
>syntax is illegal.
>
>>[1] http://www.w3.org/TR/REC-xml-names/#defaulting
>>
>>However, now look at the last example of Section 5.3.  The second
occurence
>>of <good> has attributes a and n1:a.  This is declared as legal, but if
'a'
>>inherits its namespace setting from good, then a and n1:a appear to be
>>equal.
>
>But n1:a and n1:good:a would be different.
>
>>...
>>
>>Could you please advise us on the correct interpretation (and fix the
error
>>if indeed there is one)?
>>
>>
>>     John Boyer
>>      Development Team Leader,
>>      Distributed Processing and XML
>>      PureEdge Solutions Inc.
>>      Creating Binding E-Commerce
>>      v: 250-479-8334, ext. 143  f: 250-479-3772
>>      1-888-517-2675   http://www.PureEdge.com
>
>Donald
>
Received on Friday, 11 August 2000 20:13:34 GMT

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