<xsd:attribute name="refersTo" use="required">
  <xsd:simpleType>
    <xsd:list>
      <xsd:simpleType>
        <xsd:restriction base="referenceRef"/>
      </xsd:simpleType>
    </xsd:list>
  </xsd:simpleType>
</xsd:attribute>

<xsd:attributeGroup name="refersreq">
  <xsd:annotation>
    <xsd:documentation>
      <type>Attlist</type>
      <name>refersreq</name>
      <comment>This attribute creates a connection between the element and an element of the Akoma Ntoso ontology to which it refers. In elements using this attribute definition the refersTo attribute is required</comment>
    </xsd:documentation>
  </xsd:annotation>
  <xsd:attribute name="refersTo" use="required">
    <xsd:simpleType>
      <xsd:list>
        <xsd:simpleType>
          <xsd:restriction base="referenceRef"/>
        </xsd:simpleType>
      </xsd:list>
    </xsd:simpleType>
  </xsd:attribute>
</xsd:attributeGroup>