diagram {
  title = "Legend"

  boundary {
    title = "A boundary"

    function f {
      title = "function"
    }
    database d {
      title = "database"
    }
    io i {
      title = "io"
    }
  }

  f -> d {
    action = "Operation"
    data = "Data"
  }
  i -> f {
    data = "Data"
  }
  f -> i {
    action = "Operation"
    data = `Some data,
            and other data.`
  }
}