1. Use Case Modelling

2. Use Case Diagram Example

3. 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.

4. Use Case definition Fowler: Cockburn:
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.

5. 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”]

6. 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.

7. Use Case Diagram Example

8. Use Case Diagram Example

10. 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.

11. 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.

12. Example of a Use Case Text

13. Template of an Use Case Text

14. Steps
Define the system boundaries
Define actors
Define use cases
Define scenario’s
Describe each use case
Identify communal sub-cases

15. Use Case relationships
Generalization
Include relation
Extend relation

16. 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.

17. Use Case Diagram Example

18. 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.

19. Use Case Diagram Example

20. 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.

21. Extend and Uses relationships

22. Relationships between use cases

23. Short Summary

24. 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.

25. Core Elements

26. Core Relationships

27. Core Relationships

28. Use Case Diagram Use Cases Use Case text : Example

29. NS Ticket service Define a use case diagram of ‘NS Ticket service’
Destination
Define a use case diagram of ‘NS Ticket service’
Describe an use case.
Take ticket

30. Use Case diagram ‘NS Ticket service’

31. Use Case Actors Preconditions Description Extension Exceptions Result
Use Case
Buy OV Ticket
Actors
Traveller
Preconditions
Traveller has a valid pass
Description
Ticket device expects destination code
Traveller enters destination code
Extension point: NS ticket
Ticket device checks code and calculates the charge. Shows destination code & fare. Activates ticket machine for paying
Traveller pays (use case: Pay ticket)
Ticket device print and supplies ticket
Traveller takes ticket
Extension
Destination code = NS station.
3a. Ticket device expects ticket type
3b. Traveller enters Single/Return, Discount Y/N, Class
Exceptions
Traveller interrupt the interaction or walk away
Traveller enters an incorrect destination code
Payment is not finished off successful
Result
Traveller has ticket.
(NS can look forward to the payment)