Functional Requirements

Think of the functional requirements as things the product must do from the point of view of the business. When you talk to business stakeholders, they will describe those actions, which the product must take to complete some part of their work. You can also envision the functional requirements as being independent of any technology that might be used. In other words, they are the functional essence of the work.

Functional requirements describe what the product has to do to satisfy the work or business, and are independent of any technology used by the product.

When it's time to design a solution for the functional requirements, the designer adds technological requirements that are needed by the technology used for the solution. Technological requirements are sometimes lumped together with the business requirements, and the two are collectively referred to as "functional" requirements because they refer to functions of the design or the solution. However, it is more accurate and less confusing to separate technological requirements from functional business requirements. Functional requirements, as we use the term here, describe what the product has to do to satisfy the work or business, and are independent of any technology used by the product.

The requirements specification is intended to serve as a contract for the product to be built. Thus the functional requirements must describe in enough detail which actions the intended product will perform. To satisfy this criterion, the functional requirements must contain sufficient detail for the developer to construct the correct productthe one needed by your clientwith only the minimum of clarification and explanation from the requirements analyst and the stakeholders. Note we do not say "no additional information." If the developer has absolutely no questions, then you have done too much work and provided too detailed a requirements specification. We explain this point further as we proceed.