This is a class diagram example that shows the use of qualifier. If an association attribute is unique within a set of related objects, then it is a qualiﬁer. A qualiﬁer is a value that selects a unique object from the set of related objects across an association. Lookup tables and arrays may be modelled as qualiﬁed associations. Qualiﬁers are important for modeling names and identiﬁcation codes. Qualiﬁers also model indexes in a design model.