All engineering disciplines use models to develop the products they intend to build.
Requirements models play an integral part in the discovery of requirements. Once discovered, the requirements are clarified and proven by applying the modelling rules. Once verified, the requirements models are used as specifications for the designers and builders of the system. You can describe a system by what it is, and by what it does. Beyond this innocent description of what the system must do, lies a complex set of rules, procedures, data and functions.