Sequence Diagrams

Sequence diagrams show process flow.

Elements

Dispatching calls:

• solid arrows dispatch
• dotted arrows return data
• box the timeline to show lifetime of a dispatch

Frame

• use frames for:
  • opt optional actions, followed by [condition]
  • loop looping behaviour, followed by [num loops] or [condition]
  • alt alternative actions, followed by [condition]

Tools

draw.io

• Free-form diagrams, good support for sequence diagrams

websequencediagrams.com

• Fast and automatically formatted
• Uses code defintions, like:

  title MotorControl
  actor A
  A->+SpeedControl: update(t, setpoint)
  SpeedControl->+Sensor: getSample()
  Sensor-->-SpeedControl: sensorData
  SpeedControl->Estimator: update(t, sensorData)
  opt t - tLast > ControlPeriod
  SpeedControl->+Estimator: getState()
  Estimator-->-SpeedControl: stateData
  SpeedControl->+Regulator: regulate(stateData, setpoint)
  Regulator-->-SpeedControl: commandTorque
  SpeedControl->Motor: actuate(commandTorque)