These issues constitute a clear, yet incomprehensive, argument to claim that
the transition from the customer’s needs to the requirements and then from
the requirements to the functional specifications is critical and therefore requires
an adequate level of detail and formalism in the investigation. In the engineering
design literature, these needs and requirements have been regularly investigated for the last two decades. However, a formal distinction between needs and requirements has not yet been consolidated (Ericson, M€uller,
Larsson, & Stark, 2009). In fact, the FunctioneBehavioureStructure (FBS) framework (Gero & Kannengiesser, 2004), which also constitutes a reference in the description of the design processes, explicitly refers to the requirements (R) of a design problem but in a very simplistic manner, without considering
the difference between Needs and Requirements.