Version: (using KDE KDE 3.5.8) Installed from: Ubuntu Packages I quite frequently use association classes. An association class "hangs off of" or modifies a relationship between two other classes. In the diagram on the URL below, there is a many-to-many relationship between flights and frequentfliers. When a frequentflier boards a flight, she can get some arbitrary mileagecredit (determined in some unspecified way). The mileagecredit modifies the relationship between the frequentflier and the flight - it has no existence outside of that relationship. In UML, such a class is shown as a dotted line off of the line connecting the two "main" associated classes. http://www.ibm.com/developerworks/rational/library/content/RationalEdge/sep04/bell/bell_fig11.jpg (This is similar to bug 121725.) P.S. I really like Umbrello. Intuitive and immediately useful.
*** This bug has been marked as a duplicate of bug 57588 ***