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RE: [xml-dev] which xml schema tools do it right concerning including attributes xml:lang and xml:space

From: Dare Obasanjo <dareo@microsoft.com>
Date: Wed, 17 Apr 2002 11:58:42 -0700
Message-ID: <8BD7226E07DDFF49AF5EF4030ACE0B7E05573CA7@red-msg-06.redmond.corp.microsoft.com>
To: "Paul Hermans" <paul_hermans@protext.be>, <xml-dev@lists.xml.org>
Cc: <xmlschema-dev@w3.org>
*sigh*

After confering with some of our schema folks something was brought up which adds a caveat to my comments.  

A problem arises because the normative schema for Schema (sForS) imports the schema for the XML namespace already. This means that a conformant XSD implementation acts as if the XSD for the "http://www.w3.org/2001/XMLSchema" and "http://www.w3.org/XML/1998/namespace" were imported into any schema it validates. However, Paul is attempting to re-import that namespace using a different schemaLocation and XSD. According to the W3C XML Schema recommendation[0]

"NOTE: The above is carefully worded so that multiple <import>ing of the same schema document will not constitute a violation of clause 2 of Schema Properties Correct (§3.15.6), but applications are allowed, indeed encouraged, to avoid <import>ing the same schema document more than once to forestall the necessity of establishing identity component by component. Given that the schemaLocation [attribute] is only a hint, it is open to applications to ignore all but the first <import> for a given namespace, regardless of the ·actual value· of schemaLocation, but such a strategy risks missing useful information when new schemaLocations are offered."

So this means it is possible for a conformant implementation to ignore a schema author's attempt to re-import the XML namespace and redefine its components. Currently the Microsoft .NET implementation does this but does not issue any warning when it does. 


[0] http://www.w3.org/TR/xmlschema-1/#composition-schemaImport
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> -----Original Message-----
> From: Dare Obasanjo [mailto:dareo@microsoft.com] 
> Sent: Wednesday, April 17, 2002 9:25 AM
> To: Paul Hermans; xml-dev@lists.xml.org
> Cc: xmlschema-dev@w3.org
> Subject: RE: [xml-dev] which xml schema tools do it right 
> concerning including attributes xml:lang and xml:space
> 
> 
> Interesting, I was going to suggest looking at the schema For 
> Schema(sForS)[0] as a guide as to the best way of doing this 
> since it doesn't look like the W3C XML Schema recommendation 
> (prose version) clearly spells this out. On looking at the 
> sForS it looks like 
> it assumes that the XML namespace 
> (http://www.w3.org/XML/1998/namespace) is bound to the prefix 
> "xml" without ever declaring this prefix-namespaceURI 
> matching. This is in line with the XML namespaces recommendation[1]. 
>  
> So as for your first question 
>  
> 1. "Now wanting to use these attributes in other schemas some 
> tools require that the 
> namespace ="http://www.w3.org/XML/1998/namespace" is 
> explicitly declared and using the xml prefix 
> is OK." 
>  
> This is incorrect because by definition any tool that 
> supports XML namespaces assumes that namespace is defined for 
> a well-formed XML document. You shouldn't have to explicitly 
> map the "xml" prefix to the 
> "http://www.w3.org/XML/1998/namespace 
> <http://www.w3.org/XML/1998/namespace> " namespace.
>     
> 2. "Other tools refuse the prefix xml since it is reserved 
> for W3C needs and then the following works"
>  
> This is a two part answer. (a.) The XML namespaces 
> recommendation doesn't specify what should happen if one 
> tries to redefine the prefix-namespace mapping for the "xml" 
> prefix so it is understandable for a processor to disallow 
> although a clever one might just allow it if the mapping is 
> too the XML namespace (and thus a NOOP). (b.) If the 
> processor requires the XML namespace to be declared then the 
> behavior is incorrect, see the answer to (1.) above. 
>  
> 3. "Still other tools don't want the namespace declaration at all" 
>  
> This is the behavior most consistent with that of the 
> normative sForS and the XML namespace recommendation. 
>  
> However, I suggest waiting for Jeni or Henry T to pipe in 
> before taking my word for any of this. :) 
>  
> PS: xmlschema-dev is a better list for schema questions. 
>  
> [0] http://www.w3.org/TR/xmlschema-1/#normative-schemaSchema
> [1] http://www.w3.org/TR/1999/REC-xml-names-19990114/#nsc-NSDeclared
> 
> 	-----Original Message----- 
> 	From: Paul Hermans [mailto:paul_hermans@protext.be] 
> 	Sent: Wed 4/17/2002 8:14 AM 
> 	To: 'xml-dev@lists.xml.org' 
> 	Cc: 
> 	Subject: [xml-dev] which xml schema tools do it right 
> concerning including attributes xml:lang and xml:space
> 	
> 	
> 
> 	Having in a separate schema file 
> 	<?xml version="1.0"?> 
> 	<schema targetNamespace="http://www.w3.org/XML/1998/namespace" 
> 	          xmlns:xml="http://www.w3.org/XML/1998/namespace" 
> 	          xmlns="http://www.w3.org/2001/XMLSchema" > 
> 
> 	        <attribute name="lang" type="language"/> 
> 
> 	        <attribute name="space" default="preserve"> 
> 	                <simpleType> 
> 	                        <restriction base="NCName"> 
> 	                                <enumeration value="default"/> 
> 	                                <enumeration value="preserve"/> 
> 	                        </restriction> 
> 	                </simpleType> 
> 	        </attribute> 
> 
> 	        <attributeGroup name="specialAttrs"> 
> 	                <attribute ref="xml:lang"/> 
> 	                <attribute ref="xml:space"/> 
> 	        </attributeGroup> 
> 	</schema> 
> 
> 	Now wanting to use these attributes in other schemas 
> some tools require that the 
> 	namespace ="http://www.w3.org/XML/1998/namespace" is 
> explicitly declared and using the xml prefix 
> 	is OK. 
> 
> 	<schema targetNamespace="XXXX" 
> 	        xmlns:xxx="XXXX" 
> 	        xmlns="http://www.w3.org/2001/XMLSchema" 
> 	-->     xmlns:xml="http://www.w3.org/XML/1998/namespace" 
> 	        elementFormDefault="qualified" 
> 	        attributeFormDefault="unqualified"> 
> 	        
> 	        <import 
> namespace="http://www.w3.org/XML/1998/namespace" 
> schemaLocation="xml_tva.xsd"/> 
> 
> 
> 	Other tools refuse the prefix xml since it is reserved 
> for W3C needs and then the following works 
> 
> 	<schema targetNamespace="XXXX" 
> 	        xmlns:xxx="XXXX" 
> 	        xmlns="http://www.w3.org/2001/XMLSchema" 
> 	-->     xmlns:x="http://www.w3.org/XML/1998/namespace" 
> 	        elementFormDefault="qualified" 
> 	        attributeFormDefault="unqualified"> 
> 	        
> 	        <import 
> namespace="http://www.w3.org/XML/1998/namespace" 
> schemaLocation="xml_tva.xsd"/> 
> 
> 	Still other tools don't want the namespace declaration at all 
> 
> 	<schema targetNamespace="XXXX" 
> 	        xmlns:xxx="XXXX" 
> 	        xmlns="http://www.w3.org/2001/XMLSchema" 
> 	-->     
> 	        elementFormDefault="qualified" 
> 	        attributeFormDefault="unqualified"> 
> 
> 	Which one is the correct way ? 
> 
> 
> 	Paul 
> 
> 	        
> 
> 
Received on Wednesday, 17 April 2002 14:59:27 GMT

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