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 -- dfdl-wg mailing list dfdl-wg@ogf.org https://www.ogf.org/mailman/listinfo/dfdl-wg Unless stated otherwise above: IBM United Kingdom Limited - Registered in England and Wales with number 741598. Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU -- dfdl-wg mailing list dfdl-wg@ogf.org https://www.ogf.org/mailman/listinfo/dfdl-wg Unless stated otherwise above: IBM United Kingdom Limited - Registered in England and Wales with number 741598. Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU -- dfdl-wg mailing list dfdl-wg@ogf.org https://www.ogf.org/mailman/listinfo/dfdl-wg Unless stated otherwise above: IBM United Kingdom Limited - Registered in England and Wales with number 741598. 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