Usage   A usage is a type of dependency and therefore a directed relationship between one or more clients (tail end) and one or more suppliers (arrowhead end). The elements at the tail end (clients) require the elements at the arrowhead end (supplier) in some way. This requirement may be that the elements need the other elements to be able to perform their function in a running system. It may also be an implementation dependency where only one set of elements exists in the running system and the other set were needed as part of the implementation. A usage can be used as an element in its own right, although it has a number of stereotypes that make its application more precise.

Explanation

A usage is a type of dependency indicating that one or more model elements need another set of elements. The meaning of a usage relationship is quite broad and unless it is qualified with a stereotype or a description its meaning is simply that one set of elements requires the other set. It is most commonly used in its singular form, with one element at the tail end (client) of the relationship and one element at the arrowhead end (supplier). There are a number of standard stereotypes that give the usage more precise meaning. We see this concept in our daily lives; for example when a person is learning to scuba dive they have a dependency on their instructor, both the student and the instructor have a dependency on their scuba diving equipment, they both also have a dependency on the organization that fills the tanks with air. In the first case the dependency exists while they are diving, while in the second case the dependency only existed as part of the preparation.

Related Entries

Dependency  Base Type A dependency is related to a usage because it is the base element for the usage relationship. The usage specializes the more general dependency relationship, conveying that one element requires the other element in some way. There are a number of standard stereotypes that may be added to a usage that further qualify its meaning adding more precision to the less specific or standard usage relationship.