Creating an Association Class

To create an association class:

On the diagram Tool Palette, select the association class button.
Click the diagram background. This adds a regular class icon for the association class, connected with the diamond icon.
Create participant classes.
Using the association end button, connect the n-ary association with the participant classes.

Result: The source code of an association class contains appropriate tags for the association class itself, and for each of the association end classes.

To delete an association class:

Right-click an association end link, association class, or connector.
Choose Delete or Delete from View on the context menu.

Result: The whole association class construct is deleted from the diagram.