Consider the model/view/control example depicted in Figures 6-16 and 6-15.

Question

a. Redraw the collaboration diagram of Figure 6-16 as a sequence diagram.







b. Discuss how the MVC architecture helps or hurts the following design goals.

Answer 1

• Extensibility (e.g., the addition of new types of views).
The MVC helps extensibility in terms of new types of views, since neither model objects nor existing view objects
need to be modified to accommodate the new view.
• Response time (e.g., the time between a user input and the time all views have been updated)
A pure MVC hurts response time, because the view the user sees is updated only after the model has been updated.
This can be an issue for commands involving a rapid series of interactions (e.g., dragging or resizing a geometrical
shape).
• Modifiability (e.g., the addition of new attributes in the model)
The MVC helps this goal, since only the views that need to be aware of the new attribute need to be modified. All
other views can be left unchanged.
• Access control (i.e., the ability to ensure that only legitimate users can access specific parts of the model).
The MVC helps this goal, as the model is accessed using a clear interface (the public methods of the model objects)
which can be controlled, for example, using a proxy pattern for each model class.