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Describe System Behavior Using Sequence Diagrams

You can use sequence diagrams integrated with System Composer™ to describe system behaviors as the interaction between components in a sequence of message exchanges. While designing your system, use sequence diagrams as a planning tool to envision your system and later validate that your system works as designed.

These concepts are relevant for authoring sequence diagrams:

  • A sequence diagram represents the expected interaction between structural elements of an architecture as a sequence of message exchanges.

    Use sequence diagrams to describe how the parts of a system interact.

  • A lifeline is represented by a head and a timeline that proceeds down a vertical dotted line.

    The head of a lifeline represents a component in an architecture model.

  • A message sends information from one lifeline to another. Messages are specified with a message label.

    A message label has a trigger and a constraint. A trigger determines whether the message occurs. A constraint determines whether the message is valid.

  • A gate in a sequence diagram represents the root architecture of the corresponding architecture model.

    Connect messages to gates to represent architecture ports.

  • An annotation describes the elements of a sequence diagram.

    Use annotations to provide detailed explanations of elements or workflows captured by sequence diagrams.

  • A fragment indicates how a group of messages specified within execute or interact.

    A fragment is used to model complex sequences, such as alternatives, in a sequence diagram.

  • An operand is a region in a fragment. Fragments have one or more operands depending on the kind of fragment. Operands can contain messages and additional fragments.

    Each operand can include a constraint to specify whether the messages inside the operand execute. You can express the precondition of an operand as a MATLAB® Boolean expression using the input signal of a lifeline.


To learn more about how System Composer concepts apply to systems engineering design, see System Composer Concepts.

Sequence diagrams are integrated with architecture models in System Composer. The table lists topics about using sequence diagrams.

Author Sequence Diagrams InteractivelyInteractively create and edit a sequence diagram and learn terminology.
Author Sequence Diagram FragmentsLearn how to implement fragments and more about fragment semantics.
Author Sequence Diagrams to Co-Create Architecture ModelsCreate and use sequence diagrams with architecture models.
Synchronize Sequence Diagrams and Architecture ModelsLearn how to synchronize sequence diagrams with architecture models.
Simulate Sequence Diagrams for Traffic Light ExampleSimulate a sequence of message exchanges as interactions between lifelines.
Author and Simulate Basic Colors Sequence Diagram with EnumerationsAuthor and simulate a sequence diagram containing a basic colors enumeration class.

Create a sequence diagram in the Architecture Views Gallery by clicking New > Sequence Diagram.

Author sequence diagrams labeled.

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