However… even that may not be enough

• Very large vocabularies (ontologies) might require even more complex features

• • one major issue is the way classes (i.e., “concepts”) are defined.
  • for example, define a class by characterizing the value a property can have on its instances
  • • eg: allowed prices should have their currency set to €…

• OWL includes those extra features but… the inference engines become (much) more complex