To create a generalization with a read-only subclass


  1. Select an element from your model, and drag it into the diagram pane.
  2. Select a read-only element from a model.
  3. The notification window displays a WARN message as you create a subclass generalization from the read-only element to your element. The WARN message is shown below.
  4. The Select Owner dialog opens for you to choose the owner of the newly created generalization. 
  5. Click OK

The final result should look similar to the following: