Olumide wrote:   Hi,

I'd appreciate help figuring out why the schema below validates the following xml file even though it the id='3' is not unique.

          <xs:element name="a">             <xs:complexType>               <xs:attribute name="id" use="required"/>             </xs:complexType>             <xs:unique name="uniqueId-a">               <xs:selector xpath="*"/>               <xs:field xpath="@id"/>             </xs:unique>           </xs:element>

  Well, the value of the attribute @id is unique within the scope of each element a.  What you're looking for, most likely, is to have unique values for @id of all elements a children of an Item, an similar for elements b.  In this case, the following schema should do that:    <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"               elementFormDefault="qualified">       <xs:element name="Item">          <xs:complexType>             <xs:sequence maxOccurs="unbounded">                <xs:choice>                   <xs:element name="a">                      <xs:complexType>                         <xs:attribute name="id" use="required"/>                      </xs:complexType>                   </xs:element>                   <xs:element name="b">                      <xs:complexType>                         <xs:attribute name="id" use="required"/>                      </xs:complexType>                   </xs:element>                </xs:choice>             </xs:sequence>          </xs:complexType>          <xs:unique name="uniqueId-a">             <xs:selector xpath="a"/>             <xs:field xpath="@id"/>          </xs:unique>          <xs:unique name="uniqueId-b">             <xs:selector xpath="b"/>             <xs:field xpath="@id"/>          </xs:unique>       </xs:element>    </xs:schema>   Regards, -- Florent Georges http://fgeorges.org/ http://h2oconsulting.be/