XML Schema 'all' question

[Susanne Wunsch <xmldev@uriah.heep.sax.de>]

Hello,

If the following question should be discussed elsewhere please give me
a hint. Thanks.

I try to define a modular XML schema using inheritance with the
"xs:extension" mechanism.

I would like to implement such an inherited type extended by an xs:all
model group. But that fails at the "cos-all-limited" constraint .

      http://www.w3.org/TR/xmlschema-1/#cos-all-limited

Which valid alternatives exists to my non-valid implementation? What
would be the best workaround for this issue?

I attach a shortened generalised example to show my intention.

Kind regards...
Susanne
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"; 
  targetNamespace="http://www.example.org/sampleAll"; 
  xmlns="http://www.example.org/sampleAll"; elementFormDefault="qualified">

  <xs:element name="person" type="tUnsortedData"/>
  
  <xs:complexType name="tUnsortedData">
    <xs:complexContent>
      <xs:extension base="tElementWithID">
        <xs:all>
          <xs:element name="firstname" type="xs:string"/>
          <xs:element name="lastname" type="xs:string"/>
        </xs:all>
      </xs:extension>
    </xs:complexContent>
  </xs:complexType>
  
  <xs:complexType name="tElementWithID">
    <xs:sequence>
      <xs:any namespace="##other" minOccurs="0" maxOccurs="unbounded" />
    </xs:sequence>
    <xs:attribute name="id" type="xs:ID" use="required" />
    <xs:anyAttribute namespace="##other" />
  </xs:complexType>
  
</xs:schema>