D.1 Case Description

An elevator controller must ensure that an elevator system collects and delivers passengers from floor to floor as requested. In this example, the controller must control two elevator cages that can move up and down in two shafts that cross 10 floors. There are floor buttons on the floors by which a passenger can summon an elevator to the floor. Floor buttons indicate the direction in which the passenger wants to travel. There are destination buttons in the elevator cages by which a passenger who is inside an elevator cage can request to be carried to a particular floor. Each floor has a direction indicator for each of the two shafts, which shows the direction of movement of the cage in that shaft. Each cage has a location indicator that tells a passenger at which floor the cage is now.

The specification has the following structure.

• Desired functionality.

  • Mission statement

  • Function refinement tree

  • Service descriptions

  • Partial context diagram

• Subject domain.

  • Dictionary

  • Entities

  • Assumed behavior

  • Desired behavior

• Alternative requirements-level architectures.

  • Functional decomposition, Von Neumann style

    • Data flow diagram

    • Control process

  • Subject-oriented decomposition, object-oriented style

    • Architecture diagrams

    • Control processes

    • Static structure diagram fragments

D.2 Desired Functionality

Figure D.1: Mission statement of the elevator controller. The exclusions have been stated to simplify the problem. Our basic elevator controller will, for example, let a cage stop at a floor to collect passengers, even when the cage is already fully loaded. If upon entry of a person, an elevator cage is loaded too heavily, the...