text: The restrictions for a class are displayed and edited using the Class Description View shown in Figure 
  4.17. The Class Description View holds most of the information used to describe a class. The Class 
  Description View is a powerful way of describing and defining classes. It is one of the most important 
  differences between describing classes in OWL and in other models such as most object-oriented 
  programming languages. In other models there is no formal definition that describes why one class is a 
  subclass of another, in OWL there is. Indeed, the OWL classifier can actually redefine the class hierarchy 
  based on the logical restrictions defined by the user. We will see an example of this later in the tutorial. 
  
  Restrictions are also called axioms in OWL. This has the same meaning as in logic. An axiom is a 
  logical formula defined by the user rather than deduced by the reasoner. As described above, 
  in Protégé all axioms are shown in normal font whereas all inferences inferred by the reasoner 
  are highlighted in yellow. 