UML- Useage
- Usage relationships signify that not only does a client know about
the existence of a feature of a server but that it will actually send
a message to exercise that feature at some point. Ordinary associations
might never be exercised.
- e.g. The difference between an association and a usage dependency
is akin to that between knowing the address of the editor of the
Financial Times and being its Wall Street correspondent.
- Saying that two classes are associated does not imply that the
structural link between them will ever be traversed.For example,
there may be many relationships in a database that are there to support
ad hoc queries that may never be made by any user.
- A usage link means there will be some interaction or collaboration.
One class 'uses' another if it is a client to the other class acting
as a server. Any associations introduced may subsequently be replaced
by more specific usage or (more rarely) composition relationships. This
kind of relationship is also extremely important in requirements engineering
and business process modelling.
- In UML one can use a dependency labelled «uses» to represent the
idea.
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