Use cases capture the functional requirements of the system, which describe its intended behavior. Use cases are used in the early stages of development, and are primarily a goal-oriented set of interactions between external actors and the system.

The scenario for a Use Case is initiated by one of the actors, to achieve a specific a given goal through a sequence of interactions between actors and the system.

It also includes possible variants of this sequence, e.g., alternative sequences that may also satisfy the goal, as well as sequences that may lead to failure to complete the service because of exceptional behavior, error handling, etc. The system is treated as a “black box”, and the interactions with system, including system responses, are as perceived from outside the system.

It should be noted that currently, no standard template has been defined - although the Universal Modeling Language (UML) explicitly uses Use Cases. Furthermore, Use Cases are described purely informally.