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Sequence diagram uml2/27/2023 ![]() Open this sequence diagram in the viewerĮach system/object instance and actor is placed on a lifeline - a vertical dotted line - going across the top of the sequence diagram. ![]() The further you progress down a sequence diagram, the more time has elapsed and the more events have occurred. Read a sequence diagram from the top down. However, they are still programming language neutral, and thus above the level of actual code. They are are closer to the actual code as they show all cross-system messages. ![]() Sequence diagrams extend use-case diagrams - they model the series of events that a scenario or use-case must execute. They are used to plan the development or extension of a software product and complement UML class diagrams, showing which class data is passed between which elements. The events that cross system boundaries are used by objects and people (actors) to complete their processes.Īlso known as system sequence diagrams, they are one of the main types of UML diagrams. This definition is true as of UML 2, considerably different fromUML 1.x.Activation boxes, or method-call boxes, are opaque rectangles drawn on top of lifelines to represent that processesare being performed in response to the message (ExecutionSpecifications in UML).Objects calling methods on themselves use messages and add new activation boxes on top of any others to indicate afurther level of processing.Sequence diagrams show the order of messages that are passed between elements of a system to complete a particular task or use case. Solid arrows with full heads are synchronous calls, solid arrows with stick heads are asynchronous calls anddashed arrows with stick heads are return messages. These are horizontal arrows with the message name written abovethem. Forexample, the Patron sends message 'pay' to the Cashier.Half arrows indicate asynchronous method calls.Simple restaurant sequence diagramThe UML 2.0 Sequence Diagram supports similarnotation to the UML 1.x Sequence Diagram with addedsupport for modeling variations to the standard flow ofevents.Diagram building blocksIf the lifeline is that of an object, it demonstrates a role.Note that leaving the instance name blank can representanonymous and unnamed instances.Example of a UML 2 diagramIn order to display interaction, messages are used. The arrows represent messages(stimuli) from an actor or object to other objects. The dotted linesextending downwards indicate the timeline. This diagram represents a Patronordering food and wine, drinking wine then eating thefood, and finally paying for the food. This allows the specification of simple runtimescenarios in a graphical manner.For instance, the UML 1.x diagram on the rightdescribes the sequences of messages of a (simple)restaurant system. OverviewA sequence diagram shows, as parallel vertical lines(lifelines), different processes or objects that livesimultaneously, and, as horizontal arrows, the messagesexchanged between them, in the order in which theyoccur. Itis a construct of a Message Sequence Chart.Sequence diagrams are sometimes called eventdiagrams, event scenarios, and timing diagrams. ![]() Sequence diagram 1Sequence diagramA sequence diagram in Unified Modeling Language(UML) is a kind of interaction diagram that shows howprocesses operate with one another and in what order. ![]()
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