<xs:schema xmlns:mstns="http://tempuri.org/XMLSchema1.xsd" elementFormDefault="qualified" targetNamespace="http://tempuri.org/XMLSchema1.xsd" xmlns:xs="http://www.w3.org/2001/XMLSchema"> <xs:element name="Directory"> <xs:complexType> <xs:sequence> <xs:element name="Person" maxOccurs="unbounded"> <xs:complexType> <xs:attribute name="Username" type="xs:string" use="required" /> <xs:attribute name="Age" type="xs:int" use="required" /> </xs:complexType> </xs:element> </xs:sequence> </xs:complexType> <xs:unique name="MyUserNameUniqueKey"> <xs:selector xpath="mstns:Person" /> <xs:field xpath="@Username" /> </xs:unique> </xs:element> </xs:schema>