What are the three principal stages of systems engineering?

What are the three principal stages of systems engineering?
Ans: 1. Procurement or acquisition: During this stage, the purpose of a system is decided; high-level system requirements are established; decisions are made on how functionality will be distributed across hardware, software, and people; and the components that will make up the system are purchased.
2. Development: During this stage, the system is developed. Development processes include all of the activities involved in system development such as requirements definition, system design, hardware and software engineering, system integration, and testing. Operational processes are defined and the training courses for system users are designed.
3. Operation: At this stage, the system is deployed, users are trained, and the system is brought into use. The planned operational processes usually then have to change to reflect the real working environment where the system is used. Over time, the system evolves as new requirements are identified. Eventually, the system declines in value and it is decommissioned and replaced.