PrF UG slots value type instance
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The Instance Value Type
A slot of type Instance has instances as values. More specifically, when Instance is selected as the value type, you specify one or more allowed classes. An instance of the class with this slot then takes instances of the allowed classes or of their subclasses as the value(s) of the slot.
Setting the Value Type to Instance
To set the value type of a slot to Instance:
Select Instance from the Value Type menu. The Allowed Classes pane will be displayed.
Select the classes you want as allowed classes in the Select Classes dialog box. To select multiple classes, use the Ctrl (Cmd) key; to select a range, use the Shift key.
Removing an Allowed Class
To remove a class from the list of allowed classes for a slot of type Integer:
Select the classes to remove. To highlight multiple classes, use the Ctrl (Cmd) key. To highlight a range of classes, use the Shift key.
In the Newspaper example, the slot responsible_for in the class Editor takes instances of the class Employee as values.
The instance Chief_Honcho is responsible for two instances which are descended from Employee: Sports Nut and Ms Gardiner.