![]() ![]() Sequence diagrams extend use-case diagrams - they model the series of events that a scenario or use-case must execute. They are are closer to the actual code as they show all cross-system messages. However, they are still programming language neutral, and thus above the level of actual code. Read a sequence diagram from the top down. The further you progress down a sequence diagram, the more time has elapsed and the more events have occurred. Open this sequence diagram in our diagram viewerĮach system/object instance and actor is placed on a lifeline - a vertical dotted line - going across the top of the sequence diagram. The messages that pass between the lifelines are connectors - solid for an initial message or outgoing call, and dotted for a return value (optional). When a system has to perform a process that takes some time to complete, use a vertical box on the lifeline (an activation box). The box ‘starts’ when it first receives a message, and ‘ends’ when all messages have been sent/received and the process has been completed. If an object instance is deleted before the overall sequence ends, its lifeline is terminated in an X. If a call message creates a new object instance, a new lifeline is added at that point. Repetition or recursion - where part of a sequence or messages are repeated - is surrounded by a frame shape, also known as a sequence fragment. If this is a complex sub-process, break it out into a separate diagram. Tip: Place each of these sequence fragment diagrams on their own diagram page in the same diagram file. Learn more about working with multi-page diagrams in draw.ioįrames can be used to show alternate sequences - ones that only execute if a certain condition is true.Īdd a link to that diagram page on the originating frame shape. They are also used for parallel sequences or to indicate there is a critical single thread. See the section on frame labels below for how to label and use the various types of sequence fragments. There are several sequence diagram templates you can modify to start your sequence diagram faster. The UML 2.5 and UML shape libraries contain all the shapes you will need. Click More Shapes at the bottom of the left panel, enable the UML and UML 2.5 libraries in the Software section, and click Apply. Lifelines: Drag the end of a lifeline to lengthen or shorten it. ![]()
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