4.3.5. Requirements Management Process
4.3.5. Requirements Management Process
Programs should maintain a current and approved set of requirements over the entire acquisition life cycle. The Requirements Management process helps ensure delivery of capability that meets intended mission performance to the operational end user.
The end-user needs are usually identified in operational terms at the system level during implementation of the Stakeholder Requirements Definition and Requirements Analysis processes; see DAG section 4.3.10. Stakeholder Requirements Definition Process and 4.3.11. Requirements Analysis, respectively. Through the Requirements Management process, the Systems Engineer tracks requirements changes and maintains traceability of end-user needs to the system performance specification and ultimately the delivered capability. As the system design evolves to lower levels of detail, the Systems Engineer traces the high-level requirements down to the system elements through the lowest level of the design. Requirements Management provides bottom-up traceability from any derived lower-level requirement up to the applicable source (system-level requirement) from which it originates. This bidirectional traceability is the key to effective management of system requirements. It enables the development of an analytical understanding of any system-wide effects of changes to requirements for a given system element, updating requirements documentation with rationale and impacts for approved changes. At the same time, bi-directional traceability ensures that approved changes do not create any “orphaned” lower-level requirements (i.e., that all bottom-up relationships to applicable system-level requirements remain valid after the change). Bidirectional traceability also ensures that higher-level requirements are properly flowed to lower-level requirements and system element designs so that there are no "childless parent" higher-level requirements (i.e., each high-level requirement is ultimately being addressed by lower-level requirements and system element designs).
Robust Requirements Management, implemented in synchronization with the program’s Configuration Management process (see DAG section 4.3.7. Configuration Management Process), can help the program to avoid or mitigate unintended or unanticipated consequences of changes through rigorous documentation of the system performance specification. Thoughtful analysis and management of requirements can help the lay foundation for system affordability.
Activities and Products
The Program Manager should keep leadership and all stakeholders informed of cost, schedule, and performance impacts associated with requirement changes and requirements growth.
The Systems Engineer establishes and maintains a Requirements Traceability Matrix (RTM) that captures all requirements in the system performance specification, their decomposition/derivation and allocation history, and rationale for all entries and changes. The requirements should be:
- Traceable to and from the stated user needs
- Correctly allocated, with potential effects of proposed changes fully investigated, understood, and communicated to the Program Manager
- Feasibly allocated, i.e., lower-level system elements cannot have the same or wider tolerance bands as those of the higher-level system elements into which they are incorporated
All affected stakeholders and decision makers should fully understand the effects of proposed changes to requirements at the system or system element level before they accept any changes for incorporation into the design. The RTM provides significant benefits during trade-off analysis activities since it captures the system-wide effects of proposed changes to established requirements.
DAG section 4.3.19. Tools and Techniques contains information about SE tools generally employed in the Requirements Management process. There are many commercial software packages specifically designed for the traceability aspect of Requirements Management, from top-level operational requirements down to the lowest-level system elements in the Work Breakdown Structure.
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