1.The main purpose of usecase diagram is to show who interacts with your system and the main goals they achieve with your system.it will also tell what interfaces system should have.it is also used to communicate with the end users and domain experts and also used to verify that all behavioural requirements have been captured.the main important role of a use case model is to communicate the systems functionality and behaviour to the customer or end user.
At first system boundary is defined next actors and their goals including the primaries are defined finally use case will be defined.
During design phase of development lifecycle usecases are first defined.
Use cases are used as a primary artifact for establishing the desired behaviour of the system for verifying and validating the systems architecture,for testing and for communicating among the stakeholders of the project.
2.a system event triggered by time is called temporal event.Temporal event is an event that occurs as a result of reaching a point in time.The analyst begins identifying temporal events by taking about the specific deadlines that system must accommodate.
Time is an actor of a temporal event.
Match the stakeholders and external users with actors:
- computerized door lock with keypad-primary system actor
- Rental car agent-primary business actor
- Sales manager generating regional sales report-external server actor
- Sales manager receiving regional sales report-external receiver actor
- Automatic lawn sprinkler system-time
- Driver purchasing gasoline with atm card-primary system actor
- Bank loan authorisation service-external receiver actor.
- United States postal service-external server actor