XML Schema 1.1 inheritable attributes

I've been thinking to write a small and complete example, clarifying the role of XML Schema 1.1 inheritable attributes (please see inheritable = boolean within the definition "XML Representation Summary: attribute Element Information Item" in the XSD 1.1 specification).

The XSD 1.1 inheritable attributes, are primarily useful when implementing XSD Type Alternatives.

Below is an XSD 1.1 example, and two corresponding valid XML instance documents. This example as a whole implements inheritable attributes and few other areas of XSD 1.1.

XSD document:

<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
 
   <xs:element name="X">
      <xs:complexType>
         <xs:sequence>
            <xs:element name="Y">
               <xs:alternative test="@y = 'A'">
                  <xs:complexType>
                     <xs:sequence>
                        <xs:element name="A">
                           <xs:complexType>
                              <xs:simpleContent>
                                 <xs:extension base="xs:string">
                                    <xs:attribute name="attr" type="xs:integer"/>
                                 </xs:extension>
                              </xs:simpleContent>                            
                           </xs:complexType>
                        </xs:element>
                     </xs:sequence>
                  </xs:complexType>
               </xs:alternative>
               <xs:alternative test="@y = 'B'">
                 <xs:complexType>
                     <xs:sequence>
                        <xs:element name="B">
                           <xs:complexType>
                              <xs:simpleContent>
                                 <xs:extension base="xs:string">
                                    <xs:attribute name="attr" type="xs:integer"/>
                                 </xs:extension>
                              </xs:simpleContent>                            
                           </xs:complexType>
                        </xs:element>
                     </xs:sequence>
                  </xs:complexType>            
               </xs:alternative>
            </xs:element>
         </xs:sequence>
         <xs:attribute name="y" inheritable="true">
            <xs:simpleType>
               <xs:restriction base="xs:string">
                 <xs:enumeration value="A"/>
                 <xs:enumeration value="B"/>
               </xs:restriction>
            </xs:simpleType>
         </xs:attribute>
      </xs:complexType>
   </xs:element>
 
</xs:schema>


XML document 1:

<?xml version="1.0"?>
<X y="A">
  <Y>
    <A attr="1">hello</A>
  </Y>
</X>

XML document 2:

<?xml version="1.0"?>
<X y="B">
  <Y>
    <B attr="1">hello</B>
  </Y>
</X>

The XML instance documents shown above should be validated with the XSD document provided.

Following is little explanation with respect to the semantics of this example:
An inheritable attribute "y" is defined on element "X". The XSD type of element "Y" is chosen at runtime (i.e at validation time), depending on the value of this attribute. Please notice that, how an attribute defined on element "X" makes the definition of attribute accessible to element "Y" in the schema document.

I hope that, this blog post is useful.