1 <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">

     2 

     3   <xsd:element name="itemList" type="itemListType">

     4     <xsd:unique name="itemAttr">

     5       <xsd:selector xpath="item"/>

     6       <xsd:field    xpath="@uniqueAttr"/>

     7     </xsd:unique>

     8 

     9     <xsd:key name="itemValueKey">

    10       <xsd:selector xpath="item"/>

    11       <xsd:field    xpath="."/>

    12     </xsd:key>

    13 

    14     <xsd:keyref name="itemKeyRef" refer="itemValueKey">

    15       <xsd:selector xpath="itemRef"/>

    16       <xsd:field    xpath="."/>

    17     </xsd:keyref>

    18   </xsd:element>

    19   

    20   <xsd:element name="item" type="itemType"/>

    21 

    22   <xsd:attribute name="uniqueAttr" type="xsd:string"/>

    23 

    24   <xsd:attribute name="unparsedEntityAttr" type="xsd:ENTITIES"/>

    25 

    26   <xsd:complexType name="itemListType">

    27     <xsd:sequence>

    28       <xsd:element ref="item" maxOccurs="unbounded"/>

    29       <xsd:element name="itemRef" type="xsd:string" maxOccurs="unbounded"/>

    30     </xsd:sequence>

    31   </xsd:complexType>

    32 

    33   <xsd:complexType name="itemType">

    34     <xsd:simpleContent>

    35       <xsd:extension base="xsd:string">

    36         <xsd:attribute ref="uniqueAttr" use="required"/>

    37       </xsd:extension>

    38     </xsd:simpleContent>

    39   </xsd:complexType>

    40 

    41 </xsd:schema>