Problem with abstract complex type in substitution group.

Question

Hi all,
I have three xsds, A, B, C.XSD respectively. A.xsd:There is a substitution group and its complex type declared as abstract and element that uses them. B.xsd has the same structure as A except that it has complex type derived from complex type from A. C.xsd is same as B.xsd.
The xml files of A and B validate but not of C.
It gives the following error:
This file is not valid. Unexpected element'signatureString' in element author. Expected signatureString,signatureText.
Any help at the earliest is greatly appreciated.
the code of each xsds is as follows:
A.XSD:
<?xml version="1.0" encoding="ISO-8859-1"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:PARTICIPATION="Participation" targetNamespace="Participation">
     <!-- ================================================= -->
     <!-- Package: Participation -->
     <!-- ================================================= -->
     <!-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->
     <!-- Class: <<ST>> SignatureString -->
     <!-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->
     <xs:element name="signatureString" type="PARTICIPATION:SignatureString" substitutionGroup="PARTICIPATION:signatureText"/>
     <xs:complexType name="SignatureString">
          <xs:complexContent>
               <xs:extension base="PARTICIPATION:SignatureText">
                    <xs:attribute name="value" type="xs:string" use="required"/>
               </xs:extension>
          </xs:complexContent>
     </xs:complexType>
     <!-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->
     <!-- Class: SignatureText -->
     <!-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->
     <xs:element name="signatureText" type="PARTICIPATION:SignatureText" abstract="true"/>
     <xs:complexType name="SignatureText" abstract="true"/>
</xs:schema>
B.xsd:
<?xml version="1.0" encoding="ISO-8859-1"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:CM3202="Common3202" xmlns:PARTICIPATION="Participation" targetNamespace="Common3202">
     <xs:import namespace="Participation" schemaLocation="Datatypes3203/RDT/Participation.xsd"/>
     <!-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->
     <!-- Class: <<Participation>> PractitionerParticipation -->
     <!-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->
     <xs:element name="practitionerParticipation" type="CM3202:PractitionerParticipation" abstract="true"/>
     <xs:complexType name="PractitionerParticipation" abstract="true">
          <xs:sequence>
               <!--xs:element name="signatureText" type="PARTICIPATION:SignatureText" minOccurs="0"/-->
               <xs:element ref="PARTICIPATION:signatureText"/>
               </xs:sequence>
     </xs:complexType>
     <!-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->
     <!-- Class: <<Participation>> Author -->
     <!-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->
     <xs:element name="author" type="CM3202:Author" substitutionGroup="CM3202:practitionerParticipation"/>
     <xs:complexType name="Author">
          <xs:complexContent>
               <xs:extension base="CM3202:PractitionerParticipation"/>
          </xs:complexContent>
     </xs:complexType>
</xs:schema>
C.xsd
<?xml version="1.0" encoding="ISO-8859-1"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:VS3203="VitalSigns3203" xmlns:CM3202="Common3202" targetNamespace="VitalSigns3203">
     <xs:import namespace="Common3202" schemaLocation="Common3202.xsd"/>
     <!-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->
     <!-- Class: <<Observation>> VitalSignsObservationEvent -->
     <!-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->
     <xs:element name="vitalSignsObservationEvent" type="VS3203:VitalSignsObservationEvent"/>
     <xs:complexType name="VitalSignsObservationEvent">
          <xs:sequence>
               <xs:element name="author" type="CM3202:Author" minOccurs="0">
               </xs:element>
          </xs:sequence>
     </xs:complexType>
</xs:schema>

Answer 1

Hi all,
This seems to be a bug unless someone of you have a solution.
Also I ma new to xml/xsd world, so could someone please give the differences between xsi:type vs substitution groups with both element and complex type being abstract. Can this scenario be accomplished by usuage of choice groups.
Also can anyone suggest any other good xml forums.
Please let me know.
Thanks in advance.