A project plan is established and maintained as the basis for managing the project.
A project plan is a formal, approved document used to manage and control the execution of the project. It is based on project requirements and established estimates.
The project plan should consider all phases of the project lifecycle. Project planning should ensure that all plans affecting the project are consistent with the overall project
plan.
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CMMI-ACQ 1.2
4. 
SG 2 Develop a Project Plan