After the Constraint element is created, you must apply: «validationRule» stereotype. It is derived from the «invariant » stereotype. It expands the Constraint properties with the ability to specify the following information: severity level (for sorting/filtering), abbreviation string (a short string, for easy recognition) and error message (complete description of error explanation). How to specify the validation rules properties >> To apply a stereotype, do one of the following: On the diagram pane, select an element and in that element's name area, type the stereotype name between brackets « ». The element's name comes after the stereotype. If you want to name the element Books and assign it the «table» stereotype, in the element's name area type the following: «table» Books. The name completion for the stereotypes works in the name editing mode, press Ctrl+Spacebar or Ctrl+Backspace to get a list of available stereotypes. You can change the order of the stereotypes applied to the element. The symbol style of the last stereotype in the list will be applied to the element.