text=A usage relationship is a type of dependency relationship in which one model element requires the presence of another model element (or set of model elements) for its full implementation or operation. The model element that requires the presence of another model element is the consumer in the relationship, and the model element whose presence is required is the supplier. Usage relationships include call, create, friend usage, instantiate, and send relationships.
The two model elements that participate in a usage relationship must be in the same model. Although a usage relationship indicates an ongoing need, it also indicates that the connection between the two model elements is not always meaningful or present.