XML/XML Schema/notation

xs:notation and xs:enumeration

<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:notation name="pdf" public="application/pdf" system="file:///usr/bin/acroread" />
  <xs:simpleType name="graphicalFormat">
    <xs:restriction base="xs:NOTATION">
      <xs:enumeration value="pdf" />
    </xs:restriction>
  </xs:simpleType>
</xs:schema>