To create a foundation for the overall testable requirements estimate, develop the initial requirements inventory.  The initial requirements inventory identifies the high level requirements (HLRs) associated with each type of requirement within the project.

The HLR level is the most generalized breakdown of requirements of the system.  This level corresponds to major system functions or business processes.  These functions are usually known and so this is generally not an estimate, but a known quantity.  Although, some HLRs such as Audit and Control, and Usability and Performance are often omitted from the requirements/design but assumed by the end users.  If that is the case, they should be explored as HLRs and estimated.  This begins the top-down identification of the requirements inventory.  Figure 7 illustrates a system which includes HLRs for accounting, a bank interface, and reporting.

Visio 2000 Drawing

High Level Requirements Diagram
Figure 7

These requirements are then plugged into the Requirements Sizing Matrix as the estimate's foundation.