The coordinator looks to see if all the checkers called back. If not, the coordinator does nothing. If they have, and all of them are successful, as in this case, then the coordinator notifies the Transaction that all is well. Figure 6-2 introduces a number of new elements to sequence diagrams. First, you s ee activations , which appear explicitly when a method is active because it is either executing or waiting for a subroutine to return.
Many designers use activations all the time.
I find they don't add much to procedural execution, so I use them only in concurrent situations. The half-arrowheads indicate an asynchronous message. An asynchronous message does not block the caller, so it can carry on with its own processing. An asynchronous message can do one of three things. Create a new object Communicate with a thread that is already running Object deletion is shown with a large X .