Bass.book Page i Thursday, March 20, 2003 7:21 PM Software Architecture in Practice STehcirodn Edd Eitdioitnio n i The SEI Series in Software Engineering Visit informit.com/sei for a complete list of available products. The SEI Series in Software Engineering represents is a collaborative undertaking of the Carnegie Mellon Software Engineering Institute (SEI) and Addison-Wesley to develop and publish books on software engineering and related topics. The common goal of the SEI and Addison-Wesley is to provide the most current information on these topics in a form that is easily usable by practitioners and students. Books in the series describe frameworks, tools, methods, and technologies designed to help organizations, teams, and individuals improve their technical or management capabilities. Some books describe processes and practices for developing higher-quality software, acquiring programs for complex systems, or delivering services more effectively. Other books focus on software and system architecture and product-line development. Still others, from the SEI’s CERT Program, describe technologies and practices needed to manage software and network security risk. These and all books in the series address critical problems in software engineering for which practical solutions are available. Software Architecture in Practice Third Edition Len Bass Paul Clements Rick Kazman ▲ Addison-Wesley ▼▼ Upper Saddle River, NJ • Boston • Indianapolis • San Francisco New York • Toronto • Montreal • London • Munich • Paris • Madrid Capetown • Sydney • Tokyo • Singapore • Mexico City ThTTe hhSEeeI S SSerEiEesI I i nSS Seoefrtriweiaesres Ei ninng Si nSeoeorfitnfwtgwaarere E Engnignieneereinrigng Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. 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Second printing, May 2013 00FMBass.indd 4 5/6/13 12:38 PM Contents Preface xv Reader’s Guide xvii Acknowledgments xix Part ONE INtrOductION 1 cHaPtEr 1 What Is Software architecture? 3 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 cHaPtEr 2 Why Is Software architecture Important? 25 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 v vi Contents 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 cHaPtEr 3 the Many contexts of Software architecture 39 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 Part tWO QualIty attrIbutES 61 cHaPtEr 4 understanding Quality attributes 63 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 Contents vii 4.8 For Further Reading 77 4.9 Discussion Questions 77 cHaPtEr 5 availability 79 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 cHaPtEr 6 Interoperability 103 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 cHaPtEr 7 Modifiability 117 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 cHaPtEr 8 Performance 131 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 cHaPtEr 9 Security 147 9.1 Security General Scenario 148 9.2 Tactics for Security 150 viii Contents 9.3 A Design Checklist for Security 154 9.4 Summary 156 9.5 For Further Reading 157 9.6 Discussion Questions 158 cHaPtEr 10 testability 159 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 cHaPtEr 11 usability 175 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 cHaPtEr 12 Other Quality attributes 185 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 cHaPtEr 13 architectural tactics and Patterns 203 13.1 Architectural Patterns 204 13.2 Overview of the Patterns Catalog 205 13.3 Relationships between Tactics and Patterns 238 Contents ix 13.4 Using Tactics Together 242 13.5 Summary 247 13.6 For Further Reading 248 13.7 Discussion Questions 249 cHaPtEr 14 Quality attribute Modeling and analysis 251 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 Part tHrEE arcHItEcturE IN tHE lIfE cyclE 271 cHaPtEr 15 architecture in agile Projects 275 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 cHaPtEr 16 architecture and requirements 291 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