Once gray-box details have been added to the textual use case description, more elaborate sequence diagrams can be created to reveal the internal work ings of the system. Instead of showing the interaction between actors and a monolithic system, the system is split into analysis level objects. The responsibilities of the system are divided among the analysis level objects to achieve a finer grained sequence diagram.
There are three kinds of analysis objects, and each plays a specific role in the refined model of the system.
As the name suggests, boundary objects exist at the periphery of the system. They are on the front line, interacting with the outside world.
In the refined model, boundary objects represent ...