I tried to find a way of adding a XOR constraint between 2 (works also between 3 or more?) attributes by relationship. There seems to be no information about this detail in the BOUML manual. As shown in attached project, I can "visually" show a {XOR} constraint between a "-automaticTransmission" and a "-manualTransmission" attributes by linking the text "{XOR}" to unidirectional association arrows, using "Anchor/Class association" simple lines. While this works as a visual detail, I would like to know if there is any way to implement the {XOR} condition as a defined logic condition, something that BOUML can translate in C++ code.