Process Architecture Study: Documentation
Lift Control Problem
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An N-elevator-system is to be installed in a building with M floors. Your assignment is to design the architecture of control for the system which controls the movement of the elevators. The processors can described as follows:
  1. There is one processor at each of the N elevators. This processor controls the engine, the doors and reads the push buttons and the sensors associated with every elevator.
  2. There is one processor at each of the M floors which reads the push buttons associated with the floor.
  3. There is one processor which is able to control all requests from all push buttons.
It is your choice whether you want to design a centralized or a decentralized solution to the problem. The design has to be elaborated according to the floowing rules:
  1. Each lift has a set of buttons, 1 button for each floor. These illuminate when pressed and cause the lift to visit the corresponding floor. The illumination is canceled when the corresponding floor is visited (i.e., stopped at) by the lift.
  2. Each floor has 2 buttons (except ground and top), one to request an up-lift and one to request a down-lift. These buttons illuminate when pressed. The buttons are canceled when a lift visits the floor and is either traveling in the desired direction, or visiting the floor with no requests outstanding. In the latter case, if both floor request buttons are illuminated, only 1 should be canceled. The algorithm used to decide which to service first should minimize the waiting time for both requests.
  3. When a lift has no requests to service, it should remain at its final destination with its doors closed and await further requests (or model a ``holding'' floor).
  4. All requests for lifts from floors must be serviced eventually, with all floors given equal priority (can this be proved or demonstrated?).
  5. All requests for floors within lifts must be serviced eventually, with floors being serviced sequentially in the direction of travel (can this be proved or demonstrated?).
  6. Each lift has an emergency button which, when pressed, causes a warning signal to be sent to the site manager. The lift is then deemed ``out of service''. Each lift has a mechanism to cancel its ``out of service'' status.
It is a requirement that the description tools either use object orientation, the Phase Web paradigm or CCS. A final solution is delivered in and it should be possible to another person to evaluate the solution.