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A series of successive decomposition and derivation actions beginning with stakeholder requirements and moving through high-level design requirements to low-level design requirements to the implementation of the design. During requirements engineering, several requirements baselines are defined. These baselines include: a functional baseline that provides the basis for contracting and controlling the system design; an allocated baseline that provides performance requirements for each configuration item of the system; and a product baseline that provides a detailed design specification for system elements.
NIST SP 800-160 Vol. 1