You can add optional attributes to existing classes. This may be necessary if
NOTE: Mandatory attributes can only be defined while initially creating a class.
Click Object > Add Optional Attribute to Class.
Highlight an attribute in the Available Attributes list, and then click the right arrow.
The attribute you chose will now display in the Current Attributes list as a bolded entry.
Repeat Step 2 as needed.
If you add an attribute by mistake, highlight the attribute in the Current Attributes list, and then click the left arrow.
Choose OK.