A use case consists of a set of sequences of possible interactions between the system and the user that define the functionality to be achieved and the solutions to any errors that may be encountered. Use cases are a useful technique for identifying, clarifying and organizing system requirements. The details of a use case, other than its unique name, are not represented visually in the diagram these details are given in the narrative (textual description) of the use case.Ī use case is a list of actions or event steps that typically define the interactions between the actors’ roles and the system to achieve a goal. ATMs also need to communicate with back-end servers to obtain information about user accounts.Ī use case represents a functionality (usually a requirement) that is expected to be implemented by the system.The operator is responsible for maintaining and managing the ATM system.Using ATMs as an example, answering these questions allows us to find more actors, i.e. These questions help us abstract the actors of the system. Who will maintain and administer the system?.What other systems will the system be associated with?.Who or what other systems will the system provide data for?.From whom or what other systems will the system need to obtain data?.Who will use the system once it has been developed?.Since an actor is not necessarily a person, but may be a external system, devise or a timer, we find a more specific actor by asking the following questions Note that: The symbol for an actor does not differentiate between a primary actor and a secondary actor the difference must be inferred from the use case descriptions (also called use case narratives).Ī bank loan officer wants to review a customer’s loan application, and part of the process involves a real-time credit rating check. Secondary actors are typically called upon by the system for help and a secondary actor never initiates the use case.Primary actors initiate interactions with the system. Secondary actors are the actors that the system needs to assist in order to achieve the goals of the primary actor. Use cases document the interactions between the system and actors to achieve the goals of the primary actor. For example, when an audit is passed, the system proactively sends a letter to notify people so is the sending of the letter performed automatically by the system? This use case is actually triggered by time, then the actor is Timer for example, this use case can be seen as “automatically send a letter at 5:00 every day”, then the actor that triggers this event – sending a letter – is not the system, but actually the Timer Actor Primary vs Secondary ActorsĪ primary actor is an actor that uses the system to achieve a goal. Human vs Non-Human Actorsįrom time to time, the system is affected by various events to perform certain functions in a given situation. Most often, users are people, who are involved in the use case diagram, such as customers, employees, supervisors, etc. users, but they can actually be non-people, i.e. An actor can interact with more than one use case, and a use case can interact with more than one actor.Īctors are not necessarily people, i.e.
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