Download
1 / 31
310 likes | 398 Views
Use Case Modelling. Use Case Diagram Example. Use Case Modelling. A use case is a modelling technique used to describe what a new system should do or what an existing system already does.
E N D
Use Case Modelling • A use case is a modelling technique used to describe what a new system should do or what an existing system already does. • System developers and customers/end-users discuss a use case model. In an iterative process, this lead to a requirement specification on which all agree. • A use case diagram describes the interaction between a set of use cases and the actors involved in these use cases.
Use Case definition • Fowler: • A use case is a typical interaction that a user has with a system in order to achieve some goals. • A use case is a description of a set of sequence of actions, including variants, that a system performs to yield an observable result of value to an actor. • Cockburn: • A use case describes a system’s behavior.
Actor • An actor is someone or something that interacts with the system. It is who or what uses the system. • An actor communicates with the system by sending and receiving messages. • An actor is a role that a user plays with respect to the system. • Actors – what exists outside the system (Rumbaugh) [external “participants”/”roles”]
Use cases • A use-case is a set of sequences of actions a system performs that yield an observable result of value to a particular actor. • A use-case describes a requirement for the system, that is, what it should do, but not how it should do it. • A use-case is a set of scenarios tied together by a common user goal.
Scenario A scenario is a sequence of steps describing an interaction between a user and a system. • A scenario is an instance of a use-case. • A scenario describes a possible interaction with the system.
Scenario Example • Consider a Web-based on-line store, we might have a ‘Buy a Product’ scenario that would say this : The customer browses the catalogue and adds desired items to the shopping basket. When the customer describes the shipping and credit card information and confirms the sale. The system checks the authorization on the credit card and confirms he sale both immediately and with a follow-up mail.
Steps • Define the system boundaries • Define actors • Define use cases • Define scenario’s • Describe each use case • Identify communal sub-cases
Use Case relationships • Generalization • Include relation • Extend relation
Generalization • Generalization is used when there is one use case similar to another. • Inheriting parent behaviour, adding and overriding with the child’s behaviour. • Sub use case inherits behaviour and semantics from super use cases.
Include / Uses • Uses / Include : this realtionship is used when there is a common chunck of behaviour across more than one use case. • Base use case includes the functionality of included use case.
Extend • Extend : is similar to genralization but is used to add behaviour to the base use case at certain extension points. • A use case is optionally extended by functionality of another use case.
What is Use Case modeling? • Use Case model: a view of a system that emphasizes the behavior as it appears to outside users. A use case model partitions system functionality into transactions(“use cases’) that are meaningful to users (‘actors’) • A Use Case Diagram visualizes a use case model.
NS Ticket service Destination • Define a use case diagram of ‘NS Ticket service’ • Describe an use case. Take ticket
