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SOFTWARE LIFE-CYCLES Beyond the Waterfall Milestones The WATERFALL LIFE-CYCLE Requirements System Design Standards Detailed Design Implementation Installation & Testing Documents Maintenance Problems with the Waterfall Model sequentiality late testing paradigm

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Software life cycles l.jpg

SOFTWARE LIFE-CYCLES

Beyond the Waterfall


Slide2 l.jpg

Milestones

The

WATERFALL

LIFE-CYCLE

Requirements

System Design

Standards

Detailed Design

Implementation

Installation & Testing

Documents

Maintenance


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Problems with the Waterfall Model

  • sequentiality

  • late testing paradigm

  • late feedback

    to customer and engineer

  • minimal risk management

    for customer and engineer


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The “V” LIFE-CYCLE

Requirements

Acceptance Test

System Design

Integration Test

Detailed Design

Module Test

Implementation


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Analysis of the V-Shaped Life-Cycle

  • Improves the testing paradigm

    ==> Quality Assurance

  • Does NOT really improve:

    • sequentiality

    • feedback

    • risk management (during development)


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INCREMENTAL

DEVELOPMENT

Requirements

Global System Design

Detailed D.

Detailed D.

Detailed D.

Implem.

Implem.

Implem.

Testing

Testing

Testing

Maintenance


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Analysis of Incremental Development

  • Assumes independent subsystems!

  • Improves (by delivering smaller units):

    • feedback: stepwise

    • testing

  • Avoids monolithic product

  • Does not really improve:

    • risk management during development

    • sequentiality: subsystems


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(Rapid) Prototyping

  • Goals:

    • break away from sequentiality

    • speed up feedback

    • minimize risks for

      customer and engineer

    • incomplete but executable

    • cheap and fast


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Prototyping

  • Definition (A. Davis):

    A prototype is a partial implementation of a system, constructed primarily to enable customer, user, or developer to learn about the problem or its solution.

  • Types:

    • evolutionary / throw-away

    • horizontal / vertical


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Horizontal Prototyping

f1

fn

user

hardware


Vertical prototyping l.jpg
Vertical Prototyping

f1

fn

user

hardware


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Analysis of Pure Prototyping

  • Improvements:

    • breaks sequentiality

    • supports fast feedback

    • opportunity for risk management

  • Problems:

    • missing organisational structure

      ==> combine with a life-cycle


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The Spiral Model

  • Goals:

    • risk management

    • compatible mix between

      clear structure (life-cycle) &

      flexible prototyping

    • supports fast feedback & quality assurance


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evaluate alternatives,

identify & resolve risks

determine objectives,

alternatives,

constraints

risk analysis

p r o t o t y p e s

principles

req. plan

require-

system

ments

dev.

detailed

design

design

plan

integ.

plan

implement

plan the next

phase

test &

install

develop &

verify product


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End of Section 1c

coming up:

methodologies

for analysis &

design


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