| Boundary classes are added to sequence diagrams to show the interaction with the user or another system. In the early analysis phases, the purpose of showing boundary classes on a sequence diagram is to capture and document the interface requirements, not to show how the interface will be implemented. The actual messages from the actor to the boundary class along with their sequencing information are dependent upon the application framework that is chosen later in development; thus they will probably change as more of the "how" is added to the system. |