You're right - I did not realize that this
'no undeclaring of a non-empty prefix' rule existed.
http://www.w3.org/TR/REC-xml-names/#nsc-NoPrefixUndecl
So this is not valid:
<foo:root
xmlns:foo="www.tk.com">
<foo:child
xmlns:foo=""/>
</foo:root>
but this is valid:
<root
xmlns="www.tk.com">
<child
xmlns=""/>
</root>
So there is a way to change the default
namespace from "someURL" to "". And it should therefore
be possible to re-assign the default namespace in an element reference
so that it can refer to a global element declared in a noTargetNamespace
xsd.
regards,
Tim Kimber,
Technical Lead for IBM Integration Bus Healthcare Pack
Hursley, UK
Internet: kimbert@uk.ibm.com
Tel. 01962-816742
Internal tel. 37246742
From:
Steve Hanson/UK/IBM
To:
Tim Kimber/UK/IBM@IBMGB
Cc:
dfdl-wg@ogf.org
Date:
03/11/2014 14:38
Subject:
Re: [DFDL-WG]
Action 274 - on qnames in path expressions in DFDL
Tim, I'm not sure that you comparing
apples with apples here. Mike is asking whether xmlns:foo=""
is valid, whereas your stackoverflow link is talking about xmlns=""
and it's specific use in an XML document to undeclare the namespace in
scope. Are you sure that xmlns:foo="" is valid ?
Regards
Steve Hanson
Architect, IBM
DFDL
Co-Chair, OGF
DFDL Working Group
IBM SWG, Hursley, UK
smh@uk.ibm.com
tel:+44-1962-815848
From:
Tim Kimber/UK/IBM@IBMGB
To:
dfdl-wg@ogf.org
Date:
17/10/2014 03:55
Subject:
Re: [DFDL-WG]
Action 274 - on qnames in path expressions in DFDL
Sent by:
dfdl-wg-bounces@ogf.org
I think Eclipse must be doing something
non-standard then:
http://stackoverflow.com/questions/1587891/is-xmlns-a-valid-xml-namespace
Which version of Eclipse / Eclipse plugin are you using?
regards,
Tim Kimber,
Technical Lead for IBM Integration Bus Healthcare Pack
Hursley, UK
Internet: kimbert@uk.ibm.com
Tel. 01962-816742
Internal tel. 37246742
From: Mike
Beckerle <mbeckerle.dfdl@gmail.com>
To: Tim
Kimber/UK/IBM@IBMGB
Cc: "dfdl-wg@ogf.org"
<dfdl-wg@ogf.org>
Date: 16/10/2014
14:52
Subject: Re:
[DFDL-WG] Action 274 - on qnames in path expressions in DFDL
Tim,
How do you do this? => "You define a non-empty prefix that points
to an empty namespace, and use that prefix in the QName."
specifically, what XML text corresponds to "an empty namespace".
xmlns:foo="" isn't allowed (in eclipse anyway)
Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | www.tresys.com
Please note: Contributions to the DFDL Workgroup's email discussions are
subject to the OGF
Intellectual Property Policy
On Thu, Oct 16, 2014 at 12:58 AM, Tim Kimber <KIMBERT@uk.ibm.com>
wrote:
My off-the-cuff reactions:
- every conforming XPath processor allows a 'namespace context' to be defined.
The context defines a prefix->namespace URI mapping for zero or more
prefixes.
- namespace prefixes ( including the empty prefix ) are then interpreted
in exactly the same way as they would be in an XML document. This makes
sense, because XPaths were explicitly designed to be included within XML
documents. It would look rather strange if the prefixes within an XPath
were to be interpreted differently by a) an XML processor and b) an XPath
processor.
I think that answers most of the queries, although it raises a question
over whether the Eclipse implementation is conforming.
re: the question about empty prefixes, there is a (non-obvious) way to
refer to a noTargetNamespace global element from within a document that
has a default namespace. You define a non-empty prefix that points to an
empty namespace, and use that prefix in the QName.
regards,
Tim Kimber,
Technical Lead for IBM Integration Bus Healthcare Pack
Hursley, UK
Internet: kimbert@uk.ibm.com
Tel. 01962-816742
Internal tel. 37246742
From: Mike
Beckerle <mbeckerle.dfdl@gmail.com>
To: "dfdl-wg@ogf.org"
<dfdl-wg@ogf.org>
Date: 16/10/2014
01:41
Subject: [DFDL-WG]
Action 274 - on qnames in path expressions in DFDL
Sent by: dfdl-wg-bounces@ogf.org
I did some experiments with the XML validation built into eclipse, and
the key constraint, which has paths (in the selector and field attributes)
that refer to other parts of the XML infoset/document and so involve the
names of elements.
I also have been reading the XPath 2.0 specs including the formal semantics.
To my interpretation XPath 2.0 is pretty explicit:
An element or type QName consisting only of a local part NCName expands
to the default element/type namespace and the local part.
They don't qualify this in any way that I can find for the names used in
path steps. The formal semantics is pretty hard to understand, but this
detail seems to be swept under the rug. There would need to be specific
treatment of this in the naming environment, but I cannot find this. There
is discussion of name resolution in some of their judgements, but nothing
I can see that creates an exception for names in path steps. (Called name
tests)
What I was looking for was language that specifies something about a non-prefixed
name in a path step and that it is NOT augmented by the default namespace.
I could find no such exception.
But if I am right and this detail isn't there, i.e., If there is no such
exception, then the implementation of XPath in eclipse (which is xerces
I believe) is incorrect in the way it resolves names that appear in path
steps.
Here's how it works according to eclipse:
In xpath expressions in the selectors and fields of unique and key constraints,
xmlns (the default namespace) is not considered as implicitly augmenting
unqualified names that appear in path steps.
An identifier in a path step that has no prefix (e.g., 'foo' in the path
'./p1:bar/foo/p2:baz') is always interpreted as identifying either
1) a child element defined by a local element declaration with form "unqualified".
or
2) this corner case: a child element defined by an element reference to
a global element declaration but only when that global element declaration
has no effective target namespace. (Use of 'effective' here rules out an
element decl inside a schema document that itself has no target namespace
but is included into a schema that has one. Such an element declaration
effectively has a target namespace, so this corner case doesn't apply.)
Case (2) here is a rather obscure corner case, but there nevertheless.
In no case (that I could construct) does the name in a path step get augmented
by a schema's default namespace (defined by xmlns="...whatever...").
The above is true for names without prefix appearing in path steps of expressions.
The QNames that are used in an XML schema to reference a global declaration
or definition (in the ref of an element ref, type attribute in a type reference,
base in a simple type derivation, etc.) are different. Those names DO pickup
a default namespace if one is defined and they have no explicit prefix
themselves. This creates a corner case for these references (to global
decls/defs) which is if a definition/declaration appears in no effective
target namespace, then there is no way to reference it at all from a schema
that has a default namespace definition surrounding the point of reference.
There is no syntactic way to turn-off use of a default namespace. (The
semantics of xpath allows for a "none" default namespace definition,
but there is no xml syntax for expressing explicitly this "none".
It is simply what you have if there is no prefix and no default namespace).
You can change which namespace the default is, but there's no way to say
explicitly "I meant this QName reference to be to something not in
any namespace.
Unless/until we can find language in some XML Schema spec indicating how
path step names (name tests) are specifically resolved, then the above
is just "how one system does it." But we may end up having to
follow precedent here from implementations.
Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | www.tresys.com
Please note: Contributions to the DFDL Workgroup's email discussions are
subject to the OGF
Intellectual Property Policy
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