Re: Parsing a MODS-document with validation fails

> 2. The 'unusual' condition where an attribute is in a namespace, and 
> the namespace is available with a prefix, but the SAX Parser(Xerces) 
> does not set that prefix on the qName (maybe an xerces bug?)
> 3. The even more unusual condition where an attribute is in a 
> namespace, but there is no declared version of that namespace with a 
> prefix, and SAXParser has an unqualified qName
>
>
>
>   Situation 2
>
>
> The second and third examples both rely on there being a 'default' or 
> 'fixed' attribute of form="qualified" declared on an XML Schema. For 
> example with the XMLSchema:
>
> <?xml version="1.0" encoding="UTF-8"?>
> <xs:schema xmlns="myns"
>          xmlns:xs="http://www.w3.org/2001/XMLSchema"  targetNamespace="myns"
>          elementFormDefault="qualified">
>    <xs:element name="doc">
>      <xs:complexType>
>        *<xs:attribute name="att" default="defval" form="qualified"/>*
>      </xs:complexType>
>    </xs:element>
> </xs:schema>
>
> With the above schema, here are two representative documents. The 
> first document is a representation of situation 2, where the SAX 
> parser 'should' know the prefix for the attribute:
>
> <ns:doc xmlns:ns="myns"
>                xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
>                xsi:schemaLocation="myns ./MySchema.xsd">
>
>
> This should be parsed by the SAXParser, and it should add in the 
> 'default' attribute 'att' as part of the startElement() call. The 
> resulting 'parsed' document 'should' look like:
>
> <ns:doc *ns:att="defval"*
>                xmlns:ns="myns"
>                xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
>                xsi:schemaLocation="myns ./MySchema.xsd">
>
>
> But, using xerces, the SAXParser is giving the 'co-ordinates' of the 
> 'att' attribute as   localname=att    qName=att    value=defval    
> URI=myns
>
> This is situation 2, where it would 'make sense' for the parser to 
> specify the qName as 'ns:att' instead of just 'att'.
This is what XSD 1.1 has to say about the attribute that is added to the 
InfoSet (Part 1, section 3.4.5.1):

<quote>
[prefix]
If the {attribute declaration} has a ·non-absent· {target namespace} N, 
then a namespace prefix bound to N in the [in-scope namespaces] property 
of the element information item in the ·post-schema-validation infoset·. 
If the {attribute declaration}'s {target namespace} is ·absent·, then 
·absent·.
If more than one prefix is bound to N in the [in-scope namespaces], it 
is ·implementation-dependent· which of those prefixes is used.
</quote>

In this case the attribute declaration has a target namespace, and the 
namespace prefix bound to N in the instance is "ns", so this prefix 
should be used in the InfoSet and should be reflected in the SAX events 
passed to the ContentHandler. I think this Xerces behaviour is incorrect.
>
>
>   Situation 3
>
>
> Situation 3 is like situation 2, but gives the SAXParser less 
> information to go on. This situation uses the exact same XMLSchema as 
> situation2, only it does not declare a 'prefixed' namespace, just a 
> 'default' namespace.
>
> <doc xmlns="myns"
>                xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
>                xsi:schemaLocation="myns ./MySchema.xsd">
>
> In this case, we expect the default attribute 'att' to be added to the 
> schema, but in the 'myns' namespace. Unfortunately there is *NO* 
> declaration for that namespace which is 'prefixed'.
>
> The following is the *wrong* result (att attribute should be in 'myns' 
> namespace!):
>
> <doc *att="defval"*
>                xmlns="myns"
>                xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
>                xsi:schemaLocation="myns ./MySchema.xsd">
>
> The real question is 'What is the correct result'....? Is the 
> following 'correct' ?
>
> <doc *attns0:att="defval" xmlns:attns0="myns"*
>                xmlns="myns"
>                xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
>                xsi:schemaLocation="myns ./MySchema.xsd">
>
>
>
Yes, I think the latter is correct, but the XSD 1.1 spec is not clear 
about this case. I will raise a bug. I think the answer is that in the 
Infoset produced by the schema processor, an implementation-defined 
prefix should be used; allocation of a prefix should be job of the 
schema processor, not the consumer of the Infoset.

Unfortunately the Infoset spec is rather weak on defining constraints. 
XDM is clearer: see http://www.w3.org/TR/xpath-datamodel/ section 6.3.1 
which states "in the node-name of an attribute node, if a namespace URI 
is present then a prefix must also be present". A consumer of the data 
model is entitled to expect these constraints to be satisfied.

I have raised an XSD 1.1 bug: 
http://www.w3.org/Bugs/Public/show_bug.cgi?id=13750

Michael Kay

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