Question

The following XML schema fails to validate with following XML instance document. Is there any way to rewrite the schema so the instance document validates, within the given constraints?

Constraints

• The attribute cannot be local to the element
• The instance document must be unchanged

(Invalid) Schema

<?xml version="1.0" encoding="utf-8"?>
<xs:schema targetNamespace="http://tempuri.org/XMLSchema.xsd"
    elementFormDefault="qualified"
    xmlns="http://tempuri.org/XMLSchema.xsd"
    xmlns:xs="http://www.w3.org/2001/XMLSchema">

    <xs:attribute name="sample-attribute" type="xs:string" />

    <xs:element name="sample-element">
        <xs:complexType>
            <xs:attribute ref="sample-attribute" use="required" />
        </xs:complexType>
    </xs:element>
</xs:schema>

Instance

<?xml version="1.0" encoding="utf-8"?>
<sample-element xmlns="http://tempuri.org/XMLSchema.xsd" sample-attribute="test" />

Answer 1

Namespaces in XML states that “The namespace name for an unprefixed attribute name always has no value”; on the other hand you constrained the attribute not to be local, so the only way to do it (credit goes to @GrahamHannington) is to wrap it in an attribute group, thus allowing the attribute definition to be reused without being qualified.