María Victoria Cengarle Peter Graubmann Stefan Wagner Semantics of UML 2.0 Interactions with Variabilities. 141-155 2006 160 Electr. Notes Theor. Comput. Sci. http://dx.doi.org/10.1016/j.entcs.2006.05.020 db/journals/entcs/entcs160.html#CengarleGW06