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>