text: We have described the class Pizza to be to be a subclass of Thing and a subclass of the things that have 
  a base which is some kind of PizzaBase. Notice that these are necessary conditions — if something is a 
  Pizza it is*necessary*for it to be a member of the class Thing (in OWL, everything is a member of the 
  class Thing) and*necessary*for it to have a kind of PizzaBase. More formally, for something to be a 
  Pizza it is necessary for it to be in a relationship with an individual that is a member of the class 
  PizzaBase via the property hasBase. 
  
  4.10.3 Creating Subclasses of Pizza 
  It’s now time to add some different kinds of pizzas to our ontology. We will start off by adding a 
  MargheritaPizza, which is a pizza that has toppings of mozzarella and tomato. In order to keep our 
  ontology tidy, we will group our different pizzas under the class NamedPizza. 
  
  **Exercise 14: Create Subclasses of Pizza: NamedPizza and MargheritaPizza**
  
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  1. Select Pizza from the class hierarchy on the Classes tab. 
  
  2. Click on the Add subclass icon at the top left of the Classes tab (look back at figure 4.4 if you aren’t 
  certain). You can also move your mouse over the icons and you will see a little pop-up hint for each icon. 
  
  3. Protégé will prompt you for the name of the new subclass. Call it NamedPizza. 
  
  4. Repeat steps 1-3 this time starting with NamedPizza to create a subclass of NamedPizza. Call it 
  MargheritaPizza. 
  
  5. Add a comment to the class MargheritaPizza using the Annotations view. This is above the 
  Description view. Add the comment: A pizza that only has Mozzarella and Tomato toppings. Remember 
  that annotation properties are meta-data that can be asserted about any entity whereas object and data 
  properties can only be asserted about individuals. There are a few predefined annotation properties that 
  are included in all Protégé ontologies such as the comment property. 