A 2-element constraint 
applies to two elements, such as two classes or two associations. The constraint is shown as a dashed arrow from one element to the other with the constraint string label in braces ({ }).
An OR constraint 
indicates that any instance of a class may participate in only one association at one time. The constraint is shown as a dashed line connecting two or more associations, which must have a class in common. The line is labeled by the constraint string, OR, in braces ({ }).
Name a 2-element Constraint or OR Constraint shape and add a stereotype and other property values
Double-click the shape.
Add a stereotype to a 2-element Constraint or OR Constraint shape
Double-click the shape to which you want to add the Stereotype.
Hide the stereotype on a 2-element Constraint or OR Constraint shape
Right-click the shape, click Shape Display Options, and then clear Stereotype.
