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What do you mean by sequence diagram? Explain various terms and symbols used in a sequence diagram. Describe the following using sequence diagram : (i) asynchronous messages with/without priority. (ii) broadcast messages.explain sequence diagrams with example.

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By By Team EasyExamNotes

Sequence diagram:

A sequence diagram is a type of UML (Unified Modeling Language) diagram that illustrates how objects interact with each other in a system. It describes the flow of messages or interactions between different objects over time. Here are some key terms and symbols used in a sequence diagram.

Various terms and symbols used in sequence diagram :

  1. Class Roles or Participants: Objects in the system are represented as class roles or participants. They describe how an object behaves in a particular context.
  1. Activation or Execution Occurrence: Activation occurrences represent the time an object is busy executing a task. It is depicted as a thin gray rectangle placed vertically on the object’s lifeline.
  1. Messages: Arrows represent messages exchanged between objects. Asynchronous messages are shown with half-arrowed lines, indicating that the sender does not wait for a response before continuing its tasks. Synchronous messages are represented with full arrows.
  1. Lifelines: Vertical dashed lines indicating the object’s presence over time.
  1. Destroying Objects: Objects can be terminated early using an arrow labeled “<< destroy >>” pointing to an X, denoting object destruction.
  2. Loops: A repetition or loop within a sequence diagram is depicted as a rectangle with the exit condition placed at the bottom left corner.

Asynchronous Messages:

  • An asynchronous message is represented by a half arrowhead on the arrow.
  • In the example, a real-time system authorizes personnel to pass through electronically controlled doors using asynchronous messages.

Asynchronous Messages with Priority:

  • Messages may arrive faster than the target can process them, so they are placed in a queue with different priority levels.
  • The priority level is indicated in the message properties.

Broadcast Messages:

  • A broadcast message treats every object as a potential target, and a copy goes into the queue of every object in the system.
  • Example: A startup sequencer broadcasts a message to every object in the system to load itself.
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