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

  <xsd:simpleType name="codeType">

    <xsd:restriction base="xsd:string">

      <xsd:pattern value="[A-Z]+"/>

    </xsd:restriction>

  </xsd:simpleType>

  <xsd:element name="Test">

    <xsd:complexType>

      <xsd:sequence>

                     maxOccurs="unbounded"/>

      </xsd:sequence>

    </xsd:complexType>

  </xsd:element>

  <xsd:element name="Country">

    <xsd:complexType>

      <xsd:sequence>

                     maxOccurs="unbounded"/>

      </xsd:sequence>

                     type="codeType"

                     use="required"/>

    </xsd:complexType>

    <xsd:key name="CountryDummyKey">

      <xsd:selector xpath="."/>

      <xsd:field xpath="@code"/>

    </xsd:key>

      refer="CountryDummyKey">

      <xsd:selector xpath=".//Part"/>

      <xsd:field xpath="@country"/>

    </xsd:keyref>

  </xsd:element>

  <xsd:element name="City">

    <xsd:complexType>

      <xsd:sequence>

                     minOccurs="2"

                     maxOccurs="2"/>

      </xsd:sequence>

                     type="xsd:string"

                     use="required"/>

                     type="xsd:string"

                     use="required"/>

    </xsd:complexType>

  </xsd:element>

  <xsd:element name="Part">

    <xsd:complexType>

                    type="codeType"

                    use="required"/>

    </xsd:complexType>

  </xsd:element>

</xsd:schema>