Sequence Diagram
Key elements
Notions and their significance
All other observations that makes the UML
Sequence diagrams are a type of UML diagram that show how objects in a system or classes within code interact with each other
Particularly these diagrams show interactions in order they take place in other words, they show the sequence of events.
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If diagramming a system, that would mean all the parts of that system.
If diagramming code, that would mean all of the classes that make up the program.
Objects
Parts involved in the system
Actor
Actors are always outside the scope of the system in a sequence diagram
Actor
Actors are represented by stick figures
Objects
Are represented by rectangles
Objects to be placed in sequential order from left to right
Lifelines
Lifelines are the vertical dashed lines that show the existence of an object or actor over time
Moving down the Lifeline means that more time is passing.
Interaction between actor and objects
Message
Show the information being sent between objects sequence diagrams show the order of interactions or Sequences, and they do this by moving down the lifeline with each message
Return or reply message
Message
Always represented by a dashed line
Return lines often move from right to left
That isn't always the case
The dashed line represents a return message or a message from the receiving object back to the requesting object
A message from the receiving object back to the requesting object
Alternative frame
Symbolizes a choice between two or more message sequences
Activation boxes
Activation boxes show when and how long an object is performing a process
This shows at a glance when objects are active and when they are idle
Actors are external objects. They don't need an activation box
Fairly simple sequence diagrams can get even more complex
Diagramming code
The objects might be labeled as the names of classes, and the messages might be the methods and functions used in the code
Sequence Diagram