We define the Problem
The problem statement starts with a description of the top-level functions that the system must perform: this might be in the form of a mission statement, a concept of operations or a description of the deficiency that must be ameliorated. Most mandatory and preference requirements should be traceable to this problem statement. Acceptable systems must satisfy all the mandatory requirements. The preference requirements are traded-off to find the preferred alternatives. The problem statement should be in terms of what must be done, not how to do it. The problem statement should express the customer requirements in functional or behavioral terms. It might be composed in words or as a model. Inputs come from end users, operators, maintainers, suppliers, acquirers, owners, regulatory agencies, victims, sponsors, manufacturers and other stakeholders.