A way is presented to model and validate complex, real-time systems by describing these systems from the viewpoints of the major parties in system development: the customer, the user, and the implementer. The models representing these points of view are called, respectively, the requirements model, the operations-concept model, and the implementation model. The focus is on how the concept of operations can be formally factored into established real-time system-analysis methods in terms a nontechnical user can understand. The approach integrates and refines several real-time-oriented modeling methods, including structured analysis, finite-state machines, and threads. Modeling needs are discussed, the multiview paradigm is presented, and an extensive example of a bottle-filling system is given to illustrate the use of the method.