constraints on attributes as a validation check (ish)

I'm a bit of an XSD newbie...
 
I have a set of xml files structured thus:
<root>
    <row typ="g01">
        <r>content1a</r>
        <r>content1b</r>
    </row> 
    <row typ="g02">
        <r>content2a</r>
        <r>content2b</r>
    </row> 
    <row typ="g03">
        <r>content3a</r>
        <r>content3b</r>
    </row> 
    <row type="g05">
        <r>content4a</r>
        <r>content4b</r> 
        <r>content4c</r>
    </row>
</root>
 
I need to verify that each file contains one and one only row element of
typ="g04".
Row elements may occur in any order and more than once.
Here is the *broad form* of xsd that I am using:
 
 <xs:element name="root">
  <xs:complexType>
   <xs:choice>
    <xs:sequence>
     <xs:element name="row" type="rowOther" />
     <xs:element name="row" type="rowg05" minOccurs="1"/>
    </xs:sequence>
   </xs:choice>
  </xs:complexType>
 </xs:element>

 <xs:complexType name="rowg05" abstract="true">
  <xs:sequence>
   <xs:element name="r"/>
  </xs:sequence>
  <xs:attribute name="typ" use="required">
   <xs:simpleType>
    <xs:restriction base="xs:string">
     <xs:enumeration value="g05"/>
    </xs:restriction>
   </xs:simpleType>
  </xs:attribute>
 </xs:complexType>
 
 <xs:complexType name="rowOther" abstract="true">
  <xs:sequence>
   <xs:element name="r"/>
  </xs:sequence>
  <xs:attribute name="typ" use="required">
   <xs:simpleType>
    <xs:restriction base="xs:string">
     <xs:enumeration value="g01"/>
     <xs:enumeration value="g02"/>
     <xs:enumeration value="g03"/>
     <xs:enumeration value="g04"/>
     <!--excluded <xs:enumeration value="g05"/>-->
     <xs:enumeration value="g06"/>
    </xs:restriction>
   </xs:simpleType>
  </xs:attribute>
 </xs:complexType>

I have tried various combinations of <complexType>,
abstract/non-abstract elements and such to get a result, but keep
getting hung up on declaring a row element with different types.
 
Am I making a daft mistake?
Is this actually possible with XSD?
Should I be using a different toolset?
 
Thanks
 
Andy Harris 
UK Biobank
 


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