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3SL Reference - Sequence Diagram (sd)

Sequence Diagram (sd)

The Sequence Diagram (sd) is used to represent the interaction between structural elements (Blocks and Actors) of a system, as a sequence of message exchanges between the Blocks/Actors:

  • The sending and receiving of messages
  • The start and completion of execution specifications
  • The creation and destruction of object instances

Sequence Diagrams are composed of Block/Actor Lifelines and the Message Events that are exchanged between the Lifelines. The Lifeline symbol has a trailing dashed line that represents the object's timeline where the time flows top to bottom.

Sequence Diagram Lifeline Object

A message is shown on an sd as a line with different arrowheads and annotations depending on the type of message (synchronous or asynchronous). The logic needed to produce and/or consume the identified messages can be optionally shown on the sd as Execution Specifications.

Sequence Diagram execution specifications