Why is the 'null-namespace' expected for an xml element that was defined to 'have' a namespace in the schema?

Question

The following xml document and schema was boiled down from a much larger schema in which the problem occured first:

The xml document:

<f2b:Foo xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:f2b="http://www.outerfoospace.com/schemas/foo2bar" xsi:schemaLocation="http://www.outerfoospace.com/schemas/foo2bar f2b-0-0-0.xsd">
    <f2b:Bar>text</f2b:Bar>
</f2b:Foo>

The schema:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:f2b="http://www.outerfoospace.com/schemas/foo2bar" targetNamespace="http://www.outerfoospace.com/schemas/foo2bar">
    <xs:complexType name="T_Foo">
        <xs:sequence>
            <xs:element name="Bar" xmlns="f2b"/>
        </xs:sequence>
    </xs:complexType>
    <xs:element name="Foo" type="f2b:T_Foo"/>
</xs:schema>

When I validate the document against the schema, I get an error message on the <f2b:Bar>-element saying that <f2b:Bar> is not expected. To make the document valid I have to put the <Bar>-element explicitly (!) into the 'null-namespace': <Bar xmlns="">. I don't see why a null-namespaced element should be expected. The schema defines a namespace for all elements and for the <Foo>-element the f2b-namespace is indeed expected by the validator. But even if I explicitly set the namespace in the <Bar>-element definition like I did above, the validator still expects xmlns="" for the Bar-element. I tried several variations of the schema and the document to find an answer with no luck - and I simply can't guess why the hell in this special case the null-namespace is expected.

Any hint appreciated ... ekke

Answer 1

Short answer: add elementFormDefault="qualified" to the root xs:schema tag of your schema.

Longer answer: by default, only top-level "global" element declarations take on the target namespace of the schema. "Local" element declarations inside a complex type are in no namespace. You can override this for one particular local element using the form attribute on the xs:element tag, or globally for all elements using elementFormDefault on the xs:schema.