XML Schema Definition

<!DOCTYPE exam [
  <!ELEMENT exam (student,qapair*)>
            <!ATTLIST exam paper
      CDATA #REQUIRED>
            <!ELEMENT student (#PCDATA)>
            <!ELEMENT qapair (question,answer)>
            <!ATTLIST qapair 
      number CDATA #REQUIRED>
  <!ELEMENT question (#PCDATA)>
  <!ELEMENT answer (#PCDATA)>
]>

<schema>
  <element name="exam">
    <complexType>
      <sequence>
            <element student type="string"/>
            <element qapair 
          minOccurs="0" maxOccurs="unbounded">
          <complexType>
            <sequence>
              <element question type="string"/>
              <element answer type="string"/>
            </sequence>
          </complexType>
            <attribute name="number" 
             type="positiveInteger"/>
            </element>
            </sequence>
            <attribute name="paper" type="string"/>
            </complexType>
  <element>
</schema>