user { # User
  n1: circle label:"Start Request Reply"
  n3: rectangle label:"Validate Request Reply conditions"
  n5: rectangle label:"Record Request Reply outcome"
  n7: circle label:"End Request Reply"
  n1.handle(bottom) -> app.n2.handle(top) [label="Success"]
  n3.handle(bottom) -> app.n4.handle(top)
  n5.handle(bottom) -> app.n6.handle(top)
}

app { # App
  n2: rectangle label:"Receive Request Reply event"
  n4: rectangle label:"Execute Request Reply action"
  n6: diamond label:"Monitor Request Reply status"
  n2.handle(right) -> user.n3.handle(left)
  n4.handle(right) -> user.n5.handle(left) [label="Valid"]
  n6.handle(left) -> user.n5.handle(left) [label="Retry/Rejected"]
  n6.handle(right) -> user.n7.handle(bottom)
}