Reasoning OWL ontology using inverse property?

Question

I\'m using Protege v4.3 for making ontologies. I have a question about OWL ontology and DL query.

For instance, in the Pizza ontology, http://owl.cs.manchester.ac.uk

Answer 1

When you ask what are the subclasses of:

isToppingOf some American

you are asking what classes contain toppings that are necessarily used on top of American pizzas. But in the pizza ontology, no such class exists. Consider cheese toppings: Are all cheese toppings on top of some American pizzas? No, some cheese toppings are on top of Italian pizzas. The same holds for all topping classes.