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Sequence diagrams can also be called event diagrams or event scenarios.

It helps in envisioning several dynamic scenarios. However, the majority of sequence diagrams will communicate what messages are sent and the order in which they tend to occur. The sequence diagram represents the flow of messages in the system and is also termed as an event diagram. You can specify events using messages between. The focus is more on the order in which messages occur than on the message per se. These four events cover the two interaction styles described by sequence diagrams: signals and messages. Another way of looking at it is that the user is outside the scope of the program, so it doesn't make sense to return results directly. A sequence diagram models the interactions between objects in a system in sequential order over time. As mentioned the aim of a sequence diagram is to define event sequences, which would have a desired outcome. I would not have return arrows for operations by the user, such as login(), as the results are not returned to the user in the same manner as an object, but normally outputted to some kind of UI.

) do not have return arrows as they implicitly return the instantiated object In the case of methods/functions that return a result, it would indicate a value is being returned. The focus is more on the order in which messages occur than on the message per se. The return line represents the flow of control returning from a method/function call As mentioned the aim of a sequence diagram is to define event sequences, which would have a desired outcome.