Object-Oriented Software Development with UML - UNU-IIST ...

34 Use Cases: Describing ProcessesThus, actors represent parties outside the system that collaborate with the system. Once we have identifiedall the actors of a system, we have identified the external environment of the system.4.2.2 Identifying use casesEach of the following steps for identifying use cases involves brainstorming and reviewing existing documentsof requirements specification:1. One method to identify use case is actor-based:(a) Identify the actors related to a system or organization, i.e. find and specify all the actors bylooking at which users will use the system and which other systems must interact with it.(b) For each actor, identifying the processes they initiate or participate in by looking at how theactor communicates/interacts with (or use) the system to do his work.2. A second method to identify use cases is event-based.(a) Identify the external events that a system must respond to.(b) Relate the events to actors and use cases.To identify use cases, read the existing requirements from an actor’s perspective and carry on discussionswith those who will act as actors. It will help to ask and answer a number of questions, such asWhat are the main tasks of the actor?¢Will the actor have to read/write/change any of the system information?¢Will the actor have to inform the system about outside changes?¢Does the actor wish to be informed about changes?¢For the POST application the following potential use actors and use cases can be identified:ActorCashierCustomerLog InLog OutProcesses to InitiateBuy ItemsRefund ItemsReport No. 259, July 2002UNU/IIST, P.O. Box 3058, Macau