Document:: uc-take-lift.htm

Date: 30 May, 2001; Author: Shane Sendall (LGL-DI-EPFL)


Single Cabin Elevator Control System

Use Case: Take Lift

 

Scope: Elevator Control System

Level: User Goal

Intention in Context: The User intents to go from one floor to another. The System has a single lift cabin that may service many users at any one time.

Primary Actor: User

Main Success Scenario:

1. User requests System for lift from a particular floor, also indicating the direction desired.

2. System acknowledges User's request and commands the lift to pick up User.

3. System ascertains that lift has reached User's floor+; it commands lift to stop and open its Door, and informs User.

4. User enters lift and requests System to go to a floor as destination.

5. System acknowledges User's request.

6. Door informs System of closure; System commands lift to go to destination floor.

7. System ascertains that lift has reached destination floor+; it commands lift to stop and open its Door, and informs User.

8. User exits lift.

Extensions:

2a. System determines that the lift is available at the User's floor with door open:

2a.1. System requests the Door to stay open; use case continues at step 4.

2b. System determines that the lift is available at the User's floor with door closed:

2b.1. System commands lift to open its Door; use case continues at step 4.

2c. System ascertains that the lift is currently unavailable:

2c.1. System acknowledges User's request.

2c.2. System ascertains that the lift has reached User's floor+:

2c.3. System commands lift to stop and open its Door, and informs User; use case continues at step 4.

(4-7)||a. User requests System to go to a number of additional floors*:

(4-7)||a.1. System acknowledges each additional request of User; use case continues from where it was interrupted.

4a. User does not make a request (or took the stairs)**:

4a.1. Door informs System of closure; use case ends in failure.

4b. Door informs System of closure++:

4b.1. User requests System to go to a floor as destination.

4b.2. System acknowledges User's request, and commands lift to go to destination floor; use case continues at step 7.

5a. System determines that lift is already at destination floor:

5a.1. System commands lift to open its Door, and informs User; use case continues at step 8.

8a. System determines that there are additional requests pending*: use case continues at step 6.

Notes:

* System cannot make difference between a single User making a number of requests and many Users each making a request

** undetectable by system

+ Floor Sensor indicates each floor that is reached

++ User has already entered lift (undetectable by system)


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