text: 4.13 Automated Classification and Open World Reasoning 
  Make sure that the reasoner is synchronized (the little text in the lower right corner should say Reasoner 
  active). Now switch from the Class hierarchy tab to the Class hierarchy (inferred) tab. You may notice 
  something that seems perplexing. The classes MargheritaPizza and SohoPizza both only have 
  vegetable and cheese toppings. So one might expect that the reasoner would classify them as subclasses 
  of VegetarianPizza as it recently (in section 4.11) classified them and others as subclasses of 
  CheesyPizza. The reason this didn’t happen is something called the Open World Assumption (OWA). 
  This is one of the concepts of OWL that can be most confusing for new and even experienced users 
  because it is different than the Close World Assumption (CWA) used in most other programming and 
  knowledge representation languages. 