1.3 Compatibility of the Models
The requirements and architecture models complement each other well. Processes in the requirements model can be allocated to slots in the architecture model, and this procedure can be repeated many times over going down through increasing levels of detail. Similarly, in the upward direction, the vehicle itself may be considered to be just one system within a network of systems, such as the air traffic control for a region. Again, the functional requirements for this larger system may be defined using the requirements model, and then allocated to the physical communications network using the architecture model. This leveled repetition of functional requirements definition, followed by physical allocation, is fundamental to the nature of large systems development.