Our advice
Engineering the needs and requirements of a complex system

If you had to do just one thing, it would be to describe operational scenarios for using your future system (product, service, organization). It's easy to write or imagine a story.

To define the needs of the system under study, model its context of use as an all-encompassing system, by reverse engineering its functional and physical architecture. This makes it easier to identify and define functions/services, functional interfaces (material, energy and information flows) and physical interfaces (connectors and physical links supporting flow exchanges).

A requirement = a single idea, a single sentence in the active form, such as "subject + verb in the present tense + complement". Its fulfillment must be verifiable...