www.ddss.arch.tue.nl 7m822 software requirements a use case approach 14 september 2010

www.ddss.arch.tue.nl

7M8227M822

Software RequirementsA Use Case Approach

Software RequirementsA Use Case Approach

14 September 2010


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Software RequirementsSoftware Requirements

The Rock Problem ?! [Ed Yourdon]

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Software systems natureSoftware systems nature

• Software systems by their nature are– intangible– abstract– complex– infinitely changeable

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Requirements engineeringRequirements engineering

• Get a complete description of the problem– feasibility study

• Get a complete description of the problemGet a complete description of the problem– feasibility studyfeasibility study

• Process of establishing the services that the customer requires from a system– elicitation– specification– validation

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Software developmentSoftware development

• Goal– to develop quality software that meets customers’ needs

• What is this software supposed to do?

• How, exactly, will we know when the software does exactly that and nothing else?

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Software requirementSoftware requirement

• A software requirement is a capability needed by the user to solve a problem to achieve an objective, and

is imposed on the system

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Problem domainProblem domain

• The problem domain is the home of those people (real users, other stakeholders)

whose needs must be addressed

in order to build the perfect system.

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Needs

Features

Software requirements

problemdomain

solutiondomain

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Stage

Relative cost to repair a defect

Derived from: Alan Davis, Software Requirements: objects,functions and states; Prentice-Hall, 1993

Requirements time

Design

Coding

Unit test

Acceptance test

Maintenance

.1-.2

.5

1

2

5

20

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Functional requirementsFunctional requirements

• Find the solution for the user needs by proposing objectives for the system that involves– problem definition– identifying the users– defining the solution system boundary– identifying the constraints

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Defining solutions system boundaryDefining solutions system boundary

SystemInputs Outputs

inputs / system / outputs relationship

Of concern:

1. Our system

2. Things that interact with our system

actor

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System boundarySystem boundary

Our Solution

Users

Other Systems

System Boundary

I/O

I/O

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System perspectiveSystem perspective

New Solution

Users

Catalog system

System Boundary

Library system

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Use case approach Use case approach

Lending services

User administration

Books database

Library user

Library staff

library system

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NS Ticket machine – a use case approachNS Ticket machine – a use case approach

Traveler

Purchase Ticket

Maintenance basic data

NSTake ticket

Destination

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Example Use CasesExample Use Cases

• A simple word processor is required to create new and edit existing documents.

• Also the ability to print is required.

Question?Find the system boundary, actors and use cases

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Study matterStudy matter

• Ian Sommerville Software Engineering , 6th edition – Ch.6Addison Wesley

• Dean Leffingwell & Don WidrigManaging Software Requirements, 2nd editionAddison Wesley

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www.ddss.arch.tue.nl 7m822 software requirements a use case approach 14 september 2010

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