OWL also Adds

• Cardinality Constructs
• Ability to state optional, required and/or specific number of properties.
• Constructs to combine classes
  • ability to define classes as Union, Intersection or Complement of other classes (or class combinations). Ability to declare classes as Disjoint.
• Constructs to combine properties.
  • Transitive and symmetric property definitions.
• Constructs for mapping between classes and/or ontologies.
  • Equivalence and inverse relationships
    • within ontology: CausesDisease owl:inverseOf DiseaseAssociatedWith
    • across ontology: US:soccer owl:equivalentTo UK:Football

All together, these define the ontologies that allow the structuring and linking of online data resources.