Emergent Design: The Evolutionary Nature of Professional Software Development

445 Pages·2008·7.259 MB·English

by  Scott L. Bain

Emergent Design
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Emergent Design
The Evolutionary Nature of
Professional Software Development
Scott L. Bain
Upper Saddle River, NJ • Boston • Indianapolis • San Francisco
New York • Toronto • Montreal • London • Munich • Paris • Madrid
Capetown • Sydney • Tokyo • Singapore • Mexico City
Illustrations by Andrea Chartier Bain
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ranty of any kind and assume no responsibility for errors or omissions. No liability is assumed for incidental or con-
sequential damages in connection with or arising out of the use of the information or programs contained herein.
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Library of Congress Cataloging-in-Publication Data
Bain, Scott L.
Emergent design : the evolutionary nature of professional software development / Scott L. Bain.
p. cm.
Includes index.
ISBN 978-0-321-50936-9 (hardcover : alk. paper) 1. Computer software—Development. 2. Computer
software—Development—Vocational guidance. I. Title.
QA76.76.D47B345 2008
005.1—dc22
2007050637
Copyright © 2008 Pearson Education, Inc.
All rights reserved. Printed in the United States of America. This publication is protected by copyright, and per-
mission must be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system,
or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or likewise. For
information regarding permissions, write to:
Pearson Education, Inc
Rights and Contracts Department
501 Boylston Street, Suite 900
Boston, MA 02116
Fax: [phone]
ISBN-13: 978-0-321-50936-9
ISBN-10: 0-321-50936-6
Text printed in the United States on recycled paper at Courier in Westford, Massachusetts.
First printing, March 2008
To Alan Shalloway and all instructors
and staff at Net Objectives, whose collegial
support and innovative ideas have
contributed endlessly to my
development as a technologist
and educator.
And . . .
To Andrea and Griffin, who have enriched
my entire life, and for whom I do pretty
much everything I do.
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Contents
Series Foreword___________________________________________________________xvii
Preface_____________________________________________________________________xxiii
Acknowledgments________________________________________________________xxix
About the Author__________________________________________________________xxxi
Chapter 1
Software as a Profession___________________________________1
How Long Have Human Beings Been Making Software?________________1
What Sort of Activity Is Software Development? ______________________2
What Is Missing? __________________________________________________6
Who Is Responsible?_______________________________________________8
Uniqueness_______________________________________________________9
Chapter 2
Out of the Closet, Off to the Moon _______________________11
Patterns and Professionalism in Software Development________________11
Andrea’s Closet __________________________________________________12
Off to the Moon__________________________________________________18
Forces Lead to Forces ________________________________________22
Different Forces, Different Design______________________________22
And There Are More Contextual Forces ________________________23
The Costs and Benefits _______________________________________24
On to Mars _________________________________________________26
vii
viii Contents
The Value of Patterns _____________________________________________26
Summary________________________________________________________27
Chapter 3
The Nature of Software Development__________________29
We Fail Too Much________________________________________________30
Definitions of Success_____________________________________________31
The Standish Group ______________________________________________32
Doing the Wrong Things __________________________________________34
Doing the Things Wrong __________________________________________35
Time Goes By, Things Improve_____________________________________38
One Reason: The Civil Engineering Analogy _________________________38
Giving Up Hope__________________________________________________41
Ignoring Your Mother_____________________________________________42
Bridges Are Hard, Software Is Soft__________________________________43
We Swim in an Ocean of Change___________________________________43
Accept Change___________________________________________________44
Embrace Change _________________________________________________45
Capitalize on Change _____________________________________________46
A Better Analogy: Evolving Systems ________________________________49
Summary________________________________________________________52
Chapter 4
Evolution in Code: Stage 1________________________________55
Procedural Logic Replaced with Object Structure _____________________56
The Origins of Object Orientations and Patterns ______________________56
An Example: Simple Conditionals and the Proxy Pattern ______________58
The Next Step: Either This or That__________________________________62
Why Bother? ____________________________________________________65
One Among Many________________________________________________66
Summary________________________________________________________67
Contents ix
Chapter 5
Using and Discovering Patterns_________________________69
Design from Context: More Carpentry from Scott_____________________70
Patterns Lead to Another Cognitive Perspective ______________________79
Patterns Help Give Us a Language for Discussing Design_______________79
Patterns in This Book _____________________________________________80
Summary________________________________________________________81
Chapter 6
Building a Pyramid_________________________________________83
Elements of the Profession_________________________________________83
A Visual Representation___________________________________________85
Summary________________________________________________________86
Chapter 7
Paying Attention to Qualities and Pathologies_________89
Encapsulation____________________________________________________91
Cohesion________________________________________________________91
Method Cohesion____________________________________________92
Cohesion of Perspective Level_________________________________94
Class Cohesion ______________________________________________96
How Cohesive Is Cohesive Enough? ___________________________98
Coupling ________________________________________________________99
Intentional Coupling Versus Accidental Coupling________________99
Types of Coupling __________________________________________101
Redundancy____________________________________________________106
Redundancy and Coupling___________________________________110
Testability ______________________________________________________112
Readability _____________________________________________________114
Pathologies_____________________________________________________114
Indicators of Weak Cohesion_________________________________115
Indicators of Accidental or Illogical Coupling___________________116
Indicators of Redundancy____________________________________118
Summary ______________________________________________________119