Role Changeability
Read Only specifies whether the role played by a class in an association may be modified after it has been created. By default, the role of a class in an association is considered changeable.
Example: An order includes an order line for each of the ordered products. These order lines can no longer be modified after the order has been saved.
You can indicate whether a role is changeable using the role pop-up menu or the role properties dialog box.
The Read Only characteristic of the role can have the following values:
• Add only: it is still possible to link new objects with this association, but already linked objects cannot be unlinked.
• Read Only: linked instances can no longer be unlinked. Nor is it is possible to add a new link.
• No Restriction: new instances can be linked or unlinked at any time with no constraints.
