Use Case Diagram for the Elevator System

Let’s build the elevator system’s use case diagram and understand the relationship between its main actors and functions. First, we’ll define the different elements of our system, followed by the complete use case diagram.

System

The Elevator Control system includes the physical elevator cars, floor and in-car panels, and the central controller, which manages requests and car dispatch.

Actors

Next, we will define our elevator system’s main actors.

Primary actors

• Passenger: A Passenger can do the following.

  • Call the elevator from any floor by pressing the “Up” or “Down” button on the floor panel.

  • Select a destination floor using the buttons on the in-car panel.

  • Request to open or close the doors via the “Open” and “Close” buttons on the in-car panel (when the car is stopped).

  • Trigger an emergency stop by pressing the emergency button inside the car.

Secondary actors

• Operator: The Operator can place a car in or remove it from maintenance mode; the control system responds accordingly. It can:

  • Enter maintenance mode for a selected car, causing the Elevator Control system to remove it from normal dispatch and ignore hall or in-car requests.

  • Exit maintenance mode, returning the car to the Idle state so it can resume service.

  • Receives alerts for emergencies.

Use cases

In this section, we will define the elevator’s use cases. We have listed them according to their respective interactions with a particular actor.

Passenger

• Call elevator: Press the “Up” or “Down” button on the floor panel to call an elevator (only when the car is idle or passing).

• Select destination floor: Select the desired floor using the panel inside the elevator car (only when doors are open and the car is idle).

• Request to open/close door: Press the “Open” or “Close” button on the in-car panel to request door operation (only when the car is idle).

• Trigger emergency stop: Press the “Emergency” button inside the car to immediately halt motion and alert the Support Team (allowed at any state except maintenance).

Elevator control system

• Move/stop elevator: To move up or down or to stop the elevator on a specific floor. Transitions cars between Up, Down, and Idle states; respects the maintenance state.

• Dispatch elevator: Runs the elevator-assignment algorithm on each CallElevator use case.

• Update display (inside/outside): Refresh in-car and floor displays with current floor number and travel direction within 200 ms of any state change.

• Operate doors: Open or close doors on command (only in idle state).

• Detect overload/sign alarm: When the load exceeds capacity, inhibit motion and sound/flash overload alarm until cleared.

• Notify operator: Alert the operator or security in emergency or fault scenarios.

Operator

• Enter maintenance mode: Place a car in maintenance so it ignores hall- and in-car requests.

• Exit maintenance mode: Return the car to Idle so it re-enters normal dispatch.

• Acknowledge/resolve alerts: Address alarms or emergencies (optional but useful).

Relationships

This section describes the relationships between and among actors and their use cases.

An association links an actor to a use case they participate or initiate.

In the elevator system:

• Example:

  • Passenger is associated with “Call elevator,” “Select destination floor,” “Request door open/close,” and “Trigger emergency stop.”

  • Operator is associated with “Enter Maintenance Mode” and “Exit Maintenance Mode.”

  • Elevator Control System is associated with all automation and monitoring use cases.

The table below shows the association relationship between actors and their use cases.