text: So far, we have created some simple named classes and subclasses which hopefully seem 
  intuitive and obvious. However, what does it actually mean to be a subclass of something in 
  OWL? For example, what does it mean for VegetableTopping to be a subclass of 
  PizzaTopping? In OWL subclass means*necessary implication*. I.e., if VegetableTopping is a 
  subclass of PizzaTopping then*all*instances of VegetableTopping are also instances of 
  PizzaTopping. It is for this reason that we try to have standards such as having all 
  PizzaTopping classes end with the word “Topping”. Otherwise, it might seem we are saying 
  that anything that is a kind of*Ham*like the*Ham*in your sandwich is a kind of MeatTopping or 
  PizzaTopping which is not what we mean. For large ontologies strict attention to the naming 
  of classes and other entities can prevent potential confusion and bugs. 