DAML+OIL for Application Developers - slide "Cardinality Restrictions"

RDFS provides no mechanism for limiting the number of statements containing the same subject and property

DAML+OIL allow us to specify an absolute, minimum, or maximum cardinalities, e.g.


<rdfs:Class rdf:ID="Person">
  <rdfs:subClassOf>
    <daml:Restriction>
      <daml:onProperty rdf:resource="#parent"/>
      <daml:cardinality>2</daml:cardinality>
    </daml:Restriction>
  </rdfs:subClassOf>
  <rdfs:subClassOf>
    <daml:Restriction>
      <daml:onProperty rdf:resource="#spouse"/>
      <daml:maxCardinality>1</daml:maxCardinality>
    </daml:Restriction>
  </rdfs:subClassOf>
</rdfs:Class>

indicating that a Person has 2 parents and can have at most 1 spouse

daml:cardinality is a shorthand for specifying daml:minCardinality and daml:maxCardinality
if no daml:minCardinality is specified, 0 is assumed
if no daml:maxCardinality is specified, no limit is assumed