• specification - results in precise black box description of the software component of the system.
• development - follows from black box specification by stepwise refinement and box-structured design. Concentrate on defect prevention with production of verifiably correct software.
• certification - at the same time as development, software usage specification is written which is used to certify software quality.

These 3 steps : specification, development and certification are performed by independent teams and follow an incremental model. Each increment is a usable part of the black box - external behavior. This ensures teams have control over their part.
Increments are kept to a manageable size, again ensuring teams maintain control.