A class in Protege-Frames can be Concrete, meaning it can have direct instances, or it can be Abstract, which means that while it appears in the class hierarchy, it has no direct instances. When you first create a class, by default it is Concrete. Now that we know a little more about the
Author class, we realize any instance of
Author will actually be an instance of a particular type of author, such as a news service or columnist. Therefore, we will change the
Author class to be Abstract. To change the
Author class to be an Abstract class:
- Select Author in the Class Hierarchy. In the Class Editor to the right of the Class Browser, locate the Role menu, just below the name of the class.
- Click on the Role menu and select Abstract.
- Notice that when you change the class role, the icon in front of Author changes. This new icon
indicates an abstract class in the hierarchy. A solid icon
indicates a concrete class.