17 
 
 
Figure 4.6: The Disjoint Option in the Class Description View 
 
 
 
 
 
 
4.4 Using Create Class Hierarchy 
In this section we will use Tools>Create class hierarchy to create multiple classes at once.   
OWL classes are assumed to overlap, i.e., by default they are not disjoint. This is often useful 
because in OWL, unlike in most object-oriented models, multiple inheritance is not discouraged 
and can be a powerful tool to model data. If we want classes to be disjoint, we must explicitly 
declare them to be so.  It is often a good development strategy to start with classes that are not 
disjoint and then make them disjoint once the model is more fully fleshed out as it is not always 
obvious which classes are disjoint from the beginning.