The overall purpose of Systems Engineering (SE) is to enable successful realization of the system while optimizing among competing stakeholder objectives. One way in which realization is managed is by breaking the overall effort into transformational steps, or stages, then checking for satisfactory fulfillment of system characteristics at the end of each stage, as well as checking whether risk is acceptable and the system is ready to enter other stages. Stages do not need to be executed sequentially or singularly. They can be executed multiple times as needed, and often in parallel. The critical feature of this approach is that progress is gated by specific decision points, generally called decision gates. By analogy with the stages that living things go through, called a life cycle, the set of stages for a system is termed a system life cycle. In summary, engineered systems progress in some manner through a set of stages, conceptually forming a system life cycle, with decision gates determining the completion of one stage and start of another. This part of the SE Handbook gives details for each of these parts of the system life cycle concept, as well as pointing out the role of the SE practitioner throughout a system’s life cycle. Further details can be found in ISO/IEC/IEEE 24748–1 (2018).

2.1.1 Life Cycle Characteristics

As the introduction states, life cycles are defined in terms of the ...

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