OWL Extends Other Ontologies

• You can extend an existing ontology by simply saying things about the terms in it.

<owl:Class rdf:about="#Animal">
  <rdfs:comment>
    Animals have exactly two parents, ie:
    If x is an animal, then it has exactly 2 parents 
    (but it is NOT the case that anything that has 2 
    parents is an animal).
  </rdfs:comment>
  <rdfs:subClassOf>
    <owl:Restriction owl:cardinality="2">
      <owl:onProperty rdf:resource="#hasParent"/>
    </owl:Restriction>
  </rdfs:subClassOf>
</owl:Class>

• If the ontology is already published, you would instead use the full URL.

<owl:Class 
   rdf:about="http://www.sample.com/ontologies/zoo#Animal">