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+As usual were going to illustrate these kind of diagrams by
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+using an example. In particular we are going to describe the state
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+transition diagram for part of our example, for part of
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+our course management system. And we're going to focus on the course
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+offering class. When the class is created, it enters the
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+initialization state, in which the activity performed is to initialize the
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+course. At this point, a simple case is the case in
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+which the class is cancelled, so there is a cancelled event.
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+And if that happens, the class is simply cancelled. So it
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+gets into this final state, which is the state cancelled. And
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+the activity in this case is to notify the registered students.
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+Obviously if this is the flow there will be no registered students.
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+However something else can happen when we are in this initial
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+state. So what can happen is that a student can register, so
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+in this case the add student event is triggered. And the
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+corresponding action is to set the count, in this case it would
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+be the count of students for the course offering, to one. And
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+there will be a change of state and the course offering will
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+get into this open state. And the action that will be performed
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+on entry will be to register the student. At this point more
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+students may register. So other student events might occur and notice that we
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+have a curve here that tells us this event will trigger this
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+transition only if the count is less than 10. So we're assuming
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+that we're not going to have more than 10 students just for lack
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+of a better number in our course offering. So if that
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+happens, if the count is less than ten so then the count
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+is incremented so the increment count action takes place. And the
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+system goes back into the open state, and the new student
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+is registered. Now here we have an interesting transition, because there's
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+no event triggering the transition, but simply the fact that the
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+count is equal to 10. So you can imagine this as
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+being a transition that is always enabled so can always be triggered,
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+but will be guarded. By the fact that the count has
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+to be exactly ten. So basically this transition will take place
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+only when enough students are added, such we get to count
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+them. Being incremented and being equal to ten and then the transition
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+will occur. And we will get into the closed state, in
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+which the class is no longer open because there are enough students
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+registered. And at this point, what will happen is that the
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+course will be finalized. So there will be this activity which performs
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+some operation that is needed to finalize the course. Another possibility
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+is that when we are in the open state, the course
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+is cancelled. And if the course is cancelled, in this case,
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+we go again to the cancel state. But here, the activity
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+of notifying registered students makes more sense. Because we will have
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+at least one registered student in this state, and therefore we'll
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+need to notify such student that the course offering has been
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+cancelled. Finally, is it also possible also to cancel a course
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+after it has been closed? And in this case again, the
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+same thing will happen. The class will reach the cancelled state and
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+all the students, in this case ten students, that are registered
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+for the course will be notified that the course has been cancelled.
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+So, if we look at this state transition diagram, you can
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+see that it's pretty easy to see what the evolution of objects
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+of this class can be. How they can go from their initial
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+state to various final states depending on what are the external events
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+that reach the system.