Use Case Modelling

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Use Case Modelling
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Use Case Diagram Example
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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.

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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 systems behavior.

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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

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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.

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Use Case Diagram Example
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Use Case Diagram Example
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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.

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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.

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Example of a Use Case Text
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Template of an Use Case Text
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Steps

• Define the system boundaries
• Define actors
• Define use cases
• Define scenarios
• Describe each use case
• Identify communal sub-cases

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Use Case relationships

• Generalization
• Include relation
• Extend relation

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Generalization

• Generalization is used when there is one use case
  similar to another.
• Inheriting parent behaviour, adding and
  overriding with the childs behaviour.
• Sub use case inherits behaviour and semantics
  from super use cases.

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Use Case Diagram Example
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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.

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Use Case Diagram Example
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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.

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Extend and Uses relationships
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Relationships between use cases
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Short Summary
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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.

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Core Elements
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Core Relationships
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Core Relationships
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Use Case Diagram Use CasesUse Case text
Example
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NS Ticket service
Destination

• Define a use case diagram of NS Ticket service
• Describe an use case.

Take ticket
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Use Case diagram NS Ticket service
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