Cardinality constraint in XML:

  <owl:Class rdf:ID="SVGFigure">
      <rdfs:subClassOf>
          <owl:Restriction>
              <owl:onProperty rdf:about="#ChartType"/>
              <owl:cardinality
                  rdf:dataype="...#nonNegativeInteger">
                  1
              </owl:cardinality>
          </owl:Restriction>
      </rdfs:subClassOf>
  </owl:Class>