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Universität StuttgartInstitute of Industrial Automation and Software Engineering

Prof. Dr.-Ing. Dr. h. c. P. Göhner

© 2004 IAS, Universität Stuttgart

Exercises Software Engineering for Real-Time Systems

Introduction

Exercise 8: Use Case Analysis

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Definition - Use Case

A Use Case consists of several related tasks performed by an actor aiming to reach a desired goal or to create a desired result resp.

– Sequence of related transactions performed by an actor interacting with a system aiming to get a result with a measurable value

– All the use cases document all the possibilities to make use of a system (Use Case Model)

Use Case in a Information System

– Specification of event-oriented work flows when using the software to be developed

Aims of Use Cases

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What is an actor?

– Role figured by a user of the system

– Often a person

– May also be an organisation unit or some other system

– Is always located outside the system

The Actor has an influence on the system

Notation Actor

Actor 1 Actor 2

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Use Case Template

Use Case: <Name of the use case>Goal: <Final aim of the use case assuming successful completion>Category: <primay (required, frequently needed)

| secondary (required, rarely needed)| optional (useful, needed just in case)>

Precondition: <state at the start of the use case>Postcondition Success: <expected state at normal termination of the use case>Postcondition Failure: <state after the use case has terminated due to an error>Actors: <actors involved in the use case>Triggering Event: <event that needs to occur in order to start the use case>Description: < Description of the default behavior>

1 <First action>2 <Second action>

Extensions:1a <Extension to the first action>

Alternatives:1a <Alternative to the first action>

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Use Case Diagram

Overview of relationships between actors and use cases

System

Geschäfts-prozeß2

Geschäfts-prozeß3

Geschäfts-prozeß1

Akteur3

Akteur1

Akteur2

Use Case 1

Use Case 2 Use Case 3

Notation

Actor 1

Actor 2

Actor 3

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Relationships in Use Case Diagrams

Extends and Includes relations avoid redundant use cases

- Includes Relation

- Extends Relation

Extension to an existing use case

Separation of a behavior that multiple use cases have in common

Post Invoice

Sell Service

<<includes>><<includes>>

Process subsequent

deliveryProcess Order

<<extends>>

Sell Product

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Definition - Scenario

A Scenario is a sequence of processing steps to be executed under dedicatedcircumstances.

- The processing steps have to realize the actor’s main goal and provide a complying result

- Scenarios begin with a triggering event and are continued up to the moment where the goal is reached or abandoned

– Scenarios are represented by Interaction Diagrams

– UML provides two kinds of interaction diagrams:

• Sequence Diagram• Collaboration Diagram (outside the scope of this introduction)

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Notation - Sequence Diagram

Akteur

Objektwird erzeugt

op()

Objektwirdgelöscht

op2()

:C2 :C3

op1()

op3()

Botschaft

Objekt-linie

:C1

Actor

Object is created

Object is

destroyed

Object Line

Message

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Sequence Diagram

– Two dimensions

• The vertical axis represents the time

• On the horizontal axis the objects are arranged

– Each object is represented by

• an object symbol

• a vertical dashed line (Object Linie)

– Condition

• [<Condition>] Operation()

– Iteration

• *Operation()* or [<Condition>] Operation()