16 
 
5. One last thing we want to do is to configure the reasoner. By default, the reasoner does not perform all 
possible inferences because some inferences can take a long time for large and complex ontologies. In 
this tutorial we will always be dealing with small and simple ontologies so we want to see everything the 
reasoner can do. Go to: Reasoner>Configure. This will bring up a dialog with several check boxes of 
inferences that the reasoner can perform. If they aren’t all checked then check them all. You may receive 
a warning that some inferences can take a lot of time, but you can ignore those since your ontology will 
be small. 
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4.3 Disjoint Classes 
Having added the classes Pizza, PizzaTopping, and PizzaBase to the ontology, we now want to say 
that these classes are disjoint. I.e., no individual can be an instance of more than one of those classes. In 
set theory terminology the intersection of these three classes is the empty set: owl:Nothing.  
Exercise 6: Make Pizza, PizzaTopping, and PizzaBase disjoint from each other 
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1. Select the class Pizza in the class hierarchy.    
2. Find the Disjoint With option in the Description view and select the (+) sign next to it.  See the red 
circle in figure 4.6.  
3. This should bring up a dialog with two tabs: Class hierarchy and Expression editor. You want Class 
hierarchy for now (we will use the expression editor later). This gives you an interface to select a class 
that is identical to the Class hierarchy view. Use it to navigate to PizzaBase. Hold down the shift key and 
select PizzaBase and PizzaTopping. Select OK.  
4. Do a Reasoner>Synchronize reasoner.  Then look at PizzaBase and PizzaTopping. You should see 
that they each have the appropriate disjoint axioms defined to indicate that each of these classes is disjoint 
with the other two.  
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