7. Smart Requirements, the new method of capturing, engineering and managing operational requirements, is based upon the principles of Systems Engineering. The key changes from the present "Purple Book" process are:

• a. A complete and consistent Requirement is defined but is split into User 1 and System 2 Requirements Documents (URD and SRD) reflecting user needs in the former and refining requirements on the system to fulfil those needs in the latter.
  
  
• b. The URD is updated as necessary throughout the life of the system to reflect both evolving user needs and changing assumptions. However, the URD will be baselined as necessary in order to allow project approval to take place. In particular, a baselined version of the URD, known as the Higher Level URD (HL URD) will form the Statement of Mission Needs, which will allow the development of equipment options for Initial Gate Approval.
  
  
• c. The SRD will be developed up to Main Gate, where it will be baselined for approval. Thereafter, it will be updated only as a result of trade-off decisions agreed between the Customer and the IPT leader, or later when required as the basis for in-service upgrades.
  
  
• d. Initial or Main Gate approval, the user and system requirement can be presented in an appropriate depth and scope from the underlying information base in a suitable format. Such documentation would be in the nature of a "snapshot" of the instantaneous state of the overall project requirement and would be uniquely defined and configured.
  
  
• e. Each user or system requirement is specified in terms of a single, unique and unambiguous statement, rather than the flowing textual nature of current requirements. User requirements include a statement of how, in general terms, the requirement will be verified. Each system requirement includes defined acceptance criteria.
  
  
• f. The linkage between atomised user and system requirements must be maintained by the IPT. System requirements are used as the basis of the contract with the supplier, and the linkage between the system design must be maintained by the supplier and the IPT. This will allow the impact of changes in the user requirement to be traced to the affected system requirements and system design, and to enable trade-offs in system requirements and system design to be traced back to user requirements. Linkages within the URD and SRD must also be identified, in order that interactions can be monitored.