54 
 
4. Your UI should now look similar to figure 5.5. Select OK to enter the new value. Run the reasoner.  
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Figure 5.5 hasCaloricContent for MargheritaPizza1 
 
 
 
Exercise 30: Create More Instances and Data Property Values  
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1. Remain in the Individuals by class tab. Click on other Pizzas and create instances of them (apx. 5-10) 
and then fill in their caloric content with values ranging from 200 to 800. Try to have about half of your 
pizzas higher than 400 calories and half less than 400. The UI retains the datatype from the previous use 
so once you define the first caloric content you shouldn’t need to set the datatype again but it is always a 
good idea to make sure it is correct, in this case: xsd:integer.   
2.  It is a good idea to adhere to an intuitive naming standard for your instances such as <Class 
Name><Number> as we did for MargheritaPizza1. Depending on the classes you instantiate your 
pizzas should have names like MargheritaPizza2, SohoPizza1, etc.  
One of the most common sources of errors in ontologies is to have the wrong datatype for data 
property values. The sooner you catch these errors, the easier they are to debug so it is a good 
idea to run the reasoner frequently after you enter any values.  Note that in some versions of 
Protégé 5.5. there is a minor bug where the UI may lock up due to an inconsistent data value 
(e.g., a string value in a property typed for integer). If this happens the best thing to do is save 
your work if possible, quit Protégé, and then restart it. When you restart it fix the datatype 
errors before you run the reasoner and then run the reasoner to make sure you actually have 
fixed the error.