Return values (if any) associated with previous messages.Messages (methods) invoked by these actors.This allows the specification of simple runtime scenarios in a graphical manner.Ī system sequence diagram should specify and show the following: Key elements of sequence diagram Ī sequence diagram shows, as parallel vertical lines ( lifelines), different processes or objects that live simultaneously, and, as horizontal arrows, the messages exchanged between them, in the order in which they occur. A system sequence diagram should be done for the main success scenario of the use case, and frequent or complex alternative scenarios.

All systems are treated as a black box the diagram places emphasis on events that cross the system boundary from actors to systems. Sequence diagrams are sometimes called event diagrams or event scenarios.įor a particular scenario of a use case, the diagrams show the events that external actors generate, their order, and possible inter-system events. Sequence diagrams are typically associated with use case realizations in the 4+1 architectural view model of the system under development. It depicts the processes involved and the sequence of messages exchanged between the processes needed to carry out the functionality. A sequence diagram or system sequence diagram (SSD) shows process interactions arranged in time sequence in the field of software engineering.

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