W3C home > Mailing lists > Public > w3c-ietf-xmldsig@w3.org > July to September 2000

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

From: Donald E. Eastlake 3rd <dee3@torque.pothole.com>
Date: Wed, 16 Aug 2000 12:47:04 -0400
Message-Id: <200008161647.MAA13161@torque.pothole.com>
To: "John Boyer" <jboyer@PureEdge.com>
cc: <xml-names-editor@w3.org>, <www-xml-infoset-comments@w3.org>, "XML DSig" <w3c-ietf-xmldsig@w3.org>
Hi John,

From:  "John Boyer" <jboyer@PureEdge.com>
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>
Date:  Fri, 11 Aug 2000 17:13:09 -0700
Message-ID:  <BFEDKCINEPLBDLODCODKEEFCCEAA.jboyer@PureEdge.com>
In-Reply-To:  <200008112057.QAA06998@torque.pothole.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

But the attribute is NOT "directly" in the element's namespace.  It is
in orbit around that element where the full coordinates of the element
includes the elements namespace.

>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

Why would there be an href qualified by a namespace?

>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)

The attitude of the XML authorities seems to be "Most of the time it
doesn't matter and where it does the documentation for N:E should tell
you and if it doesn't mention it, then maybe the second processing
model is better, but it really doesn't matter much and you should stop
being such a narrow minded programmer and being so algorithmic and be
happy with the under-specified fuzzyness of it all."

>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.

The fuzzy handwaving implications of the wording used in the XML
Namespaces specification is that N:A should be some sort of global
attribute which can appear in many elements while plain A is some sort
of normal local attribute to N:E.  If the text documenting N and/or E
doesn't tell you what to do here, you get to toss a coin or something.

>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.

What I meant to say was that it is a matter of point of view if you
consider attributes without prefixes to be in no namespace and to be
defined relative to their element or you considered them to have a
globally unique name composed of their name, their element's local
name, and their element's namespace if any.  The first point of view
says they are not in any namespace while the second point of view
implies they are, in some sense, in their element's namespace,
although not directly in that namespace.

>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.

Aren't XPath node tests by QName?  If you specify the namespace, it
will only look at N1:A, if you don't specify any namespace, it will
only look at A, right?

>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.

N1:A is A directly in namespace N1.  It is qualified only by N1.  A is
defined to be different because, while it can be viewed as qualified
by both E and N1 and it is defined as not being directly in namespce
N1.

>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.

Why do you say that the non-normative part "makes the two attributes
equal for the purposes of processing"?  It distinguishes them by
saying that one is in the Per-Element-Type attribute partition
associated with that element of the namesapce while the other is in
the Global attribute partition of the namesapce.

>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:

As I read it under the namesapces spec, "unqualified" attributes are
super-local, not super-global as you suggest above.

><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.

You are assuming that E is defined in both N1 and N2?  Then I think
you need to read the doucmentation of E in N1 and the documentation of
E in N2 to figure this out.  XML is just plain under-specified and no
amount of thought will change its ambiguous parts into an un-ambiguous
specifiction.

>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.

Sure, probably a good idea to add a few words to our specification to
say what should be done for such "duplicate" attributes for elements
we define.

>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 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 Wednesday, 16 August 2000 12:44:35 GMT

This archive was generated by hypermail 2.2.0 + w3c-0.29 : Thursday, 13 January 2005 12:10:10 GMT