Re: [xml] XML schema for empty NS failed to compile due to xmlns=""

[Daniel Veillard <veillard redhat com>]

On Fri, Dec 23, 2011 at 11:46:24AM +0100, Michael Ludwig wrote:
> Consider the following doc and schema:
>
>   $ cat emptyns.xml
>   <Urmel>33</Urmel>
>
>   $ cat emptyns.xsd
>   <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema";>
>       <xsd:element name="Urmel" type="Urmel_T"/>
>       <!-- Convoluted typing just for the sake of the example -->
>       <xsd:simpleType name="Urmel_T">
>           <xsd:restriction base="xsd:int"/>
>       </xsd:simpleType>
>   </xsd:schema>
>
>   $ xmllint --noout --schema emptyns.xsd emptyns.xml
>   emptyns.xml validates
>
> Now let's make a stupid edit to the schema file, add a redundant
> xmlns="" to the top-level element. This sets the empty namespace
> as the default namespace. And it is redundant because the empty
> namespace already *is* the default namespace.
>
>   $ head -1 emptyns.xsd
>   <xsd:schema xmlns="" xmlns:xsd="http://www.w3.org/2001/XMLSchema";>
>
>   $ xmllint --noout emptyns.xsd # parses just fine
>
> The schema now fails to compile:
>
>   $ xmllint --noout --schema emptyns.xsd emptyns.xml
>   Element '{http://www.w3.org/2001/XMLSchema}element', attribute
>   'type': References from this schema to components in the namespace
>   '' are not allowed, since not indicated by an import statement.
>   WXS schema emptyns.xsd failed to compile
>
> Should I add this to the bugtracker? Or is it just too stupid to
> be worthy of further attention?

  Hum, with the usual warning that I understand close to nothing to the
XSD specification, the error seems to indicate that the value of the
type attribute on the xsd:element is being checked for potential
namespace, and that the default namespace there end up applying to
"Urmel_T", and then the XSD compilation fails because that external
namespace was not declared.
  At the strict XML level that extra namespace doesn't change any of the
document structure but the interpretation of the content by the XSD
seems to be different. Someone knowing XSd well should probably chime in
and offer an educated opinion though :-)

Daniel

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