Pattern-Oriented Software Architecture For Dummies®

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Pattern-Oriented

Software

Architecture

FOR

DUMmIES‰

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by Robert Hanmer

A John Wiley and Sons, Ltd, Publication

Pattern-Oriented

Software

Architecture

FOR

DUMmIES‰

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Pattern-Oriented Software Architecture For Dummies®

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About the Author

Robert Hanmer is a director of The Hillside Group, an organization whose

mission is to improve quality of life for everyone who uses, builds, and

encounters software systems. The Hillside Group also sponsors Pattern

Languages of Programming (PLoP) software pattern conferences. Bob is

active in the software pattern community and has been program chair at

pattern conferences in the United States and overseas.

He is a consulting member of technical staff with Alcatel-Lucent near Chicago.

Within Alcatel-Lucent, Lucent Technologies, and Bell Laboratories (same

office, new company names), he is involved in development and architecture

of embedded systems, focusing especially on the areas of reliability and

performance. Previously, he designed interactive graphics systems used by

medical researchers.

Bob is the author of Patterns for Fault Tolerant Software (Wiley) and has

written or co-written 14 journal articles and several book chapters. He is a

senior member of the Association for Computing Machinery, a member of

the Alcatel-Lucent Technical Academy, and a member of the IEEE Computer

Society. He received his BS and MS degrees in Computer Science from

Northwestern University in Evanston, Illinois.

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Dedication

For Karen

Author’s Acknowledgments

First, and most important, I want to acknowledge the authors of Pattern￾Oriented Software Architecture: A System of Patterns (Wiley): Frank

Buschmann, Regine Meunier, Hans Rohnert, Peter Sommerlad, and Michael

Stal. Peter also has been helpful with questions about modern C++ and the

software architecture classroom.

Many other people answered questions, reviewed sections, or generally

consulted with me while I was writing this book. Thanks to Ademar Aguiar,

Omar Aldawud, Dan Bergen, Filipe Correia, Chuck Corwin, Jerry Dzeidzic,

Christoph Fehling, Becky Fletcher, Brian Foote, Karen Hanmer, Kenji

Hiranabe, Lise Hvatum, Satomi Joba, Dr. Ralph Johnson, Capt. U.S. Navy

(Ret.) Will H. Jordan, Steven P. Karas, Allan Kelley, Christian Kohls, Christian

Koppe, John Krallman, John Letourneau, Steffen Macke, Dennis Mancl,

Jyothish Maniyath, Veena Mendiratta, Pedro Monteiro, Karl Rehmer, Linda

Rising, Hans Rudin, Eugene Wallingford, Michael Weiss, and Joe Yoder.

Thanks to the members of my writers’ workshop group at PLoP 2011 who held

a workshop on parts of this book: Dr. Tanya L. Crenshaw, Andre Hauge, Jiwon

Kim, Alexander Nowak, Rick Rodin, YoungSu Son, and Hironori Washizaki.

The Real-World Example sidebars in the pattern chapters are based on a

workshop at the 1998 OOPSLA conference. It was organized by Michael Duell,

Linda Rising, Peter Sommerlad, and Michael Stal. Russ Frame, Kandi Frasier,

Rik Smoody, and Jun’ichi Suzuki participated in the workshop and contrib￾uted to the examples that I’ve adapted here.

Thanks also to the many people at John Wiley & Sons, including Birgit

Gruber, Chris Katsaropoulos, Elizabeth Kuball, Ellie Scott, Jim Siddle,

Kathy Simpson, Chris Webb, and the others whose names you see on the

Publisher’s Acknowledgments page.

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Publisher’s Acknowledgments

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outside the U.S. at 317-572-3993, or fax 317-572-4002.

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Contents at a Glance

Introduction ................................................................ 1

Part I: Introducing Software Architecture and Patterns... 7

Chapter 1: Software Architecture Basics........................................................................9

Chapter 2: Where Do Architectures Come From? .......................................................25

Chapter 3: What Do Software Architectures Look Like? ............................................37

Chapter 4: Software Pattern Basics...............................................................................55

Chapter 5: Seeing How Patterns Are Made and Used .................................................73

Part II: Putting Patterns to Work ................................ 83

Chapter 6: Making Sense of Patterns.............................................................................85

Chapter 7: Building Your Own Pattern Catalog ...........................................................95

Chapter 8: Choosing a Pattern.....................................................................................103

Part III: Creating Your Application Architecture......... 115

Chapter 9: Building Functionality in Layers ...............................................................117

Chapter 10: Piping Your Data through Filters............................................................137

Chapter 11: Sharing Knowledge and Results on a Blackboard ................................151

Chapter 12: Coordinating Communication through a Broker..................................171

Chapter 13: Structuring Your Interactive Application with

Model-View-Controller................................................................................................189

Chapter 14: Layering Interactive Agents with Presentation￾Abstraction-Control ....................................................................................................209

Chapter 15: Putting Key Functions in a Microkernel ................................................229

Chapter 16: Reflecting and Adapting...........................................................................245

Part IV: Designing with Other POSA Patterns............. 263

Chapter 17: Decomposing the System’s Structure ....................................................265

Chapter 18: Making a Component the Master............................................................271

Chapter 19: Controlling Access....................................................................................277

Chapter 20: Managing the System ...............................................................................285

Chapter 21: Enhancing Interprocess Communication ..............................................295

Chapter 22: Counting the Number of References ......................................................309

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Part V: The Part of Tens ........................................... 319

Chapter 23: Ten Patterns You Should Know..............................................................321

Chapter 24: Ten Places to Look for Patterns..............................................................327

Chapter 25: Ten Ways to Get Involved with the Pattern Community .....................333

Index ...................................................................... 339

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Table of Contents

Introduction ................................................................. 1

About This Book ..............................................................................................1

Conventions Used in This Book.....................................................................2

What You’re Not to Read................................................................................3

Foolish Assumptions.......................................................................................3

How This Book Is Organized..........................................................................3

Part I: Introducing Software Architecture and Patterns ...................4

Part II: Putting Patterns to Work..........................................................4

Part III: Creating Your Application Architecture ...............................4

Part IV: Designing with Other POSA Patterns ....................................5

Part V: The Part of Tens........................................................................5

Icons Used in This Book .................................................................................5

Where to Go from Here...................................................................................6

Part I: Introducing Software Architecture and Patterns ... 7

Chapter 1: Software Architecture Basics . . . . . . . . . . . . . . . . . . . . . . . . 9

Understanding Software Architecture ..........................................................9

Components of software architecture ..............................................10

Architecture document.......................................................................11

Architecture models (views)..............................................................11

Software development methods and processes..............................12

Identifying the Problem to Be Solved .........................................................13

Breaking the problem into the four attributes.................................13

Developing a problem statement.......................................................14

Defining the important use cases ......................................................15

Identifying the Requirements.......................................................................18

Defining functional requirements ......................................................19

Defining nonfunctional requirements ...............................................19

Reviewing the requirements...............................................................22

Choosing a Software System Style...............................................................24

Architectural styles .............................................................................24

Programming style...............................................................................24

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xii Pattern-Oriented Software Architecture For Dummies

Chapter 2: Where Do Architectures Come From? . . . . . . . . . . . . . . . . . 25

Understanding Architectural Styles............................................................25

Elements of styles................................................................................26

Patterns and architectural styles ......................................................26

Creating Software Architecture ...................................................................27

Deciding when to create an architecture .........................................27

Identifying problem categories ..........................................................28

Defining layers and abstractions .......................................................28

Employing enabling techniques.........................................................30

Designing your architecture...............................................................33

Documenting your work .....................................................................35

Chapter 3: What Do Software Architectures Look Like? . . . . . . . . . . 37

Examining UML Architectural Models ........................................................37

Choosing a diagram style....................................................................37

Showing different views ......................................................................38

Working with UML Diagrams .......................................................................40

Creating class diagrams......................................................................40

Showing the interactions ....................................................................44

Deploying your system .......................................................................46

Packaging up the software..................................................................47

Using use-case diagrams.....................................................................48

Choosing Your Design Tools........................................................................49

Commercial software-development tools.........................................50

Free UML tools .....................................................................................50

General drawing tools .........................................................................51

Explaining Your Software in an Architecture Document..........................52

Organizing the architecture document.............................................52

Filling in the sections...........................................................................53

Chapter 4: Software Pattern Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

What Patterns Are .........................................................................................55

Reusable designs .................................................................................56

Proven solutions ..................................................................................58

Educational tools .................................................................................58

System guides.......................................................................................59

Architectural vocabularies.................................................................59

Repositories of expertise....................................................................60

What Patterns Are Not..................................................................................60

Looking Inside Patterns ................................................................................61

Title........................................................................................................62

Problem statement ..............................................................................62

Context..................................................................................................63

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Table of Contents xiii

Forces....................................................................................................64

Solution .................................................................................................66

Other common sections......................................................................67

Understanding the Patterns Used in This Book ........................................69

The Design Patterns pattern style .....................................................70

The Pattern-Oriented Software Architecture pattern style............71

Chapter 5: Seeing How Patterns Are Made and Used . . . . . . . . . . . . 73

Creating Patterns...........................................................................................73

Coming up with the idea .....................................................................74

Confirming the Rule of Three .............................................................75

Extracting the general solution..........................................................75

Writing the pattern document ...........................................................76

Naming the pattern..............................................................................77

Getting expert reviews ........................................................................77

Keeping patterns current....................................................................80

Documenting System Architecture with Patterns.....................................81

Part II: Putting Patterns to Work................................. 83

Chapter 6: Making Sense of Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

Understanding Pattern Classifications .......................................................85

Styles .....................................................................................................86

Depth.....................................................................................................87

Other classifications............................................................................91

Grouping Patterns .........................................................................................92

Pattern collections...............................................................................92

Pattern languages ................................................................................93

Chapter 7: Building Your Own Pattern Catalog . . . . . . . . . . . . . . . . . . 95

Assembling Your Catalog .............................................................................96

Choosing a medium.............................................................................96

Identifying the problems you face.....................................................97

Finding patterns that solve your problems......................................97

Organizing the catalog in sections ....................................................98

Connecting the patterns ...................................................................100

Keeping Your Catalog Current...................................................................100

Chapter 8: Choosing a Pattern.................................103

Examining Patterns Critically.....................................................................103

Asking the right questions about patterns.....................................104

Knowing what to look for in a pattern ............................................104

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