Software Architecture in Practice

Len Bass is a Senior Principal Researcher at National ICT Australia Ltd (NICTA). He joined NICTA in 2011 after twenty-five years at the Software Engineering Institute (SEI) at Carnegie Mellon University. He is the coauthor of two award-winning books in software architecture, including Documenting Software Architectures: Views and Beyond, Second Edition (Addison-Wesley, 2011), as well as several other books and numerous papers in computer science and software engineering on a wide range of topics. Len has almost fifty years’ experience in software development and research in multiple domains, such as scientific analysis systems, embedded systems, and information systems.

Paul Clements is the Vice President of Customer Success at BigLever Software, Inc., where he works to spread the adoption of systems and software product line engineering.  Prior to this position, he was Senior Member of the Technical Staff at the SEI, where, for 17 years, he lead or co-lead projects in software product line engineering and software architecture documentation and analysis. Other books Paul has coauthored include Documenting Software Architectures: Views and Beyond, Second Edition (Addison-Wesley, 2011) and Evaluating Software Architectures:  Methods and Case Studies, (Addison-Wesley, 2002), and Software Product Lines: Practices and Patterns (Addison-Wesley, 2002).  In addition, he has also published dozens of papers in software engineering reflecting his long-standing interest in the design and specification of challenging software systems. Paul was a founding member of the IFIP WG2.10 Working Group on Software Architecture.

Rick Kazman is a Professor at the University of Hawaii and a Visiting Scientist (and former Senior Member of the Technical Staff) at the SEI. He is a coauthor of Evaluating Software Architectures: Methods and Case Studies, (Addison-Wesley, 2002). Rick’s primary research interests are software architecture, design and analysis tools, software visualization, and software engineering economics. He is also interested in human-computer interaction and information retrieval. Rick was one of the creators of several highly influential methods and tools for architecture analysis, including the SAAM (Software Architecture Analysis Method), the ATAM (Architecture Tradeoff Analysis Method), the CBAM (Cost-Benefit Analysis Method), and the Dali architecture reverse engineering tool.

Preface xv

1.1 What Software Architecture Is and What It Isn’t 4

1.2 Architectural Structures and Views 9

1.3 Architectural Patterns 18

1.4 What Makes a “Good” Architecture? 19

1.5 Summary 21

1.6 For Further Reading 22

1.7 Discussion Questions 23

2.1 Inhibiting or Enabling a System’s Quality Attributes 26

2.2 Reasoning About and Managing Change 27

2.3 Predicting System Qualities 28

2.4 Enhancing Communication among Stakeholders 29

2.5 Carrying Early Design Decisions 31

2.6 Defining Constraints on an Implementation 32

2.7 Influencing the Organizational Structure 33

2.8 Enabling Evolutionary Prototyping 33

2.9 Improving Cost and Schedule Estimates 34

2.10 Supplying a Transferable, Reusable Model 35

2.11 Allowing Incorporation of Independently Developed Components 35

2.12 Restricting the Vocabulary of Design Alternatives 36

2.13 Providing a Basis for Training 37

2.14 Summary 37

2.15 For Further Reading 38

2.16 Discussion Questions 38

3.1 Architecture in a Technical Context 40

3.2 Architecture in a Project Life-Cycle Context 44

3.3 Architecture in a Business Context 49

3.4 Architecture in a Professional Context 51

3.5 Stakeholders 52

3.6 How Is Architecture Influenced? 56

3.7 What Do Architectures Influence? 57

3.8 Summary 59

3.9 For Further Reading 59

3.10 Discussion Questions 60

4.1 Architecture and Requirements 64

4.2 Functionality 65

4.3 Quality Attribute Considerations 65

4.4 Specifying Quality Attribute Requirements 68

4.5 Achieving Quality Attributes through Tactics 70

4.6 Guiding Quality Design Decisions 72

4.7 Summary 76

4.8 For Further Reading 77

4.9 Discussion Questions 77

5.1 Availability General Scenario 85

5.2 Tactics for Availability 87

5.3 A Design Checklist for Availability 96

5.4 Summary 98

5.5 For Further Reading 99

5.6 Discussion Questions 100

6.1 Interoperability General Scenario 107

6.2 Tactics for Interoperability 110

6.3 A Design Checklist for Interoperability 114

6.4 Summary 115

6.5 For Further Reading 116

6.6 Discussion Questions 116

7.1 Modifiability General Scenario 119

7.2 Tactics for Modifiability 121

7.3 A Design Checklist for Modifiability 125

7.4 Summary 128

7.5 For Further Reading 128

7.6 Discussion Questions 128

8.1 Performance General Scenario 132

8.2 Tactics for Performance 135

8.3 A Design Checklist for Performance 142

8.4 Summary 145

8.5 For Further Reading 145

8.6 Discussion Questions 145

9.1 Security General Scenario 148

9.2 Tactics for Security 150

9.3 A Design Checklist for Security 154

9.4 Summary 156

9.5 For Further Reading 157

9.6 Discussion Questions 158

10.1 Testability General Scenario 162

10.2 Tactics for Testability 164

10.3 A Design Checklist for Testability 169

10.4 Summary 172

10.5 For Further Reading 172

10.6 Discussion Questions 173

11.1 Usability General Scenario 176

11.2 Tactics for Usability 177

11.3 A Design Checklist for Usability 181

11.4 Summary 183

11.5 For Further Reading 183

11.6 Discussion Questions 183

12.1 Other Important Quality Attributes 185

12.2 Other Categories of Quality Attributes 189

12.3 Software Quality Attributes and System Quality Attributes 190

12.4 Using Standard Lists of Quality Attributes–or Not 193

12.5 Dealing with “X-ability”: Bringing a New Quality Attribute into the Fold 196

12.6 For Further Reading 200

12.7 Discussion Questions 201

13.1 Architectural Patterns 204

13.2 Overview of the Patterns Catalog 205

13.3 Relationships between Tactics and Patterns 238

13.4 Using Tactics Together 242

13.5 Summary 247

13.6 For Further Reading 248

13.7 Discussion Questions 249

14.1 Modeling Architectures to Enable Quality Attribute Analysis 252

14.2 Quality Attribute Checklists 260

14.3 Thought Experiments and Back-of-the-Envelope Analysis 262

14.4 Experiments, Simulations, and Prototypes 264

14.5 Analysis at Different Stages of the Life Cycle 265

14.6 Summary 266

14.7 For Further Reading 267

14.8 Discussion Questions 269

15.1 How Much Architecture? 277

15.2 Agility and Architecture Methods 281

15.3 A Brief Example of Agile Architecting 283

15.4 Guidelines for the Agile Architect 286

15.5 Summary 287

15.6 For Further Reading 288

15.7 Discussion Questions 289

16.1 Gathering ASRs from Requirements Documents 292

16.2 Gathering ASRs by Interviewing Stakeholders 294

16.3 Gathering ASRs by Understanding the Business Goals 296

16.4 Capturing ASRs in a Utility Tree 304

16.5 Tying the Methods Together 308

16.6 Summary 308

16.7 For Further Reading 309

16.8 Discussion Questions 309

17.1 Design Strategy 311

17.2 The Attribute-Driven Design Method 316

17.3 The Steps of ADD 318

17.4 Summary 325

17.5 For Further Reading 325

17.6 Discussion Questions 326

18.1 Uses and Audiences for Architecture Documentation 328

18.2 Notations for Architecture Documentation 329

18.3 Views 331

18.4 Choosing the Views 341

18.5 Combining Views 343

18.6 Building the Documentation Package 345

18.7 Documenting Behavior 351

18.8 Architecture Documentation and Quality Attributes 354

18.9 Documenting Architectures That Change Faster Than You Can Document Them 355

18.10 Documenting Architecture in an Agile Development Project 356

18.11 Summary 359

18.12 For Further Reading 360

18.13 Discussion Questions 360

19.1 Architecture and Implementation 363

19.2 Architecture and Testing 370

19.3 Summary 376

19.4 For Further Reading 376

19.5 Discussion Questions 377

20.1 Architecture Reconstruction Process 381

20.2 Raw View Extraction 382

20.3 Database Construction 386

20.4 View Fusion 388

20.5 Architecture Analysis: Finding Violations 389

20.6 Guidelines 392

20.7 Summary 393

20.8 For Further Reading 394

20.9 Discussion Questions 395

21.1 Evaluation Factors 397

21.2 The Architecture Tradeoff Analysis Method 400

21.3 Lightweight Architecture Evaluation 415

21.4 Summary 417

21.5 For Further Reading 417

21.6 Discussion Questions 418

22.1 Planning 420

22.2 Organizing 422

22.3 Implementing 427

22.4 Measuring 429

22.5 Governance 430

22.6 Summary 432

22.7 For Further Reading 432

22.8 Discussion Questions 433

23.1 Decision-Making Context 438

23.2 The Basis for the Economic Analyses 439

23.3 Putting Theory into Practice: The CBAM 442

23.4 Case Study: The NASA ECS Project 450

23.5 Summary 457

23.6 For Further Reading 458

23.7 Discussion Questions 458

24.1 Competence of Individuals: Duties, Skills, and Knowledge of Architects 460

24.2 Competence of a Software Architecture Organization 467

24.3 Summary 475

24.4 For Further Reading 475

24.5 Discussion Questions 477

25.1 An Example of Product Line Variability 482

25.2 What Makes a Software Product Line Work? 483

25.3 Product Line Scope 486

25.4 The Quality Attribute of Variability 488

25.5 The Role of a Product Line Architecture 488

25.6 Variation Mechanisms 490

25.7 Evaluating a Product Line Architecture 493

25.8 Key Software Product Line Issues 494

25.9 Summary 497

25.10 For Further Reading 498

25.11 Discussion Questions 498

26.1 Basic Cloud Definitions 504

26.2 Service Models and Deployment Options 505

26.3 Economic Justification 506

26.4 Base Mechanisms 509

26.5 Sample Technologies 514

26.6 Architecting in a Cloud Environment 520

26.7 Summary 524

26.8 For Further Reading 524

26.9 Discussion Questions 525

27.1 The Ecosystem of Edge-Dominant Systems 528

27.2 Changes to the Software Development Life Cycle 530

27.3 Implications for Architecture 531

27.4 Implications of the Metropolis Model 533

27.5 Summary 537

27.6 For Further Reading 538

27.7 Discussion Questions 538

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