The requirements capture process describes what the system should do. Requirements capture results in a use-case model. The use-case model consists of actors and use-cases. Actors represent the customers or another software system. Use-cases represent the behavior of the system. The use-case description shows how the system interacts step-by-step with the actors. The use-cases function as a unifying thread throughout the system's development cycle. The same use-case model is used during requirements capture, analysis and design, and test.