Olaf Zimmermann is professor of software architecture at the Institute for Software at Eastern Switzerland University of Applied Sciences, Distinguished IT Architect at The Open Group, and co-editor of IEEE Software's Insights column. Mirko Stocker is professor of software engineering at Eastern Switzerland University of Applied Sciences, specializing on Web development and cloud solutions. Daniel L�bke is an independent coding and consulting architect who specializes in business process automation and digitization projects. Uwe Zdun is professor of software architecture at the University of Vienna, focusing on distributed systems engineering, DevOps, patterns, modeling, and empirical software engineering. Cesare Pautasso is a professor at the Universit� della Svizzera Italiana, where he leads the Architecture, Design, and Web Information Systems Engineering research group. The authors are active community members participating in pattern writer's workshops, shepherding other authors, serving on program committees, and chairing conferences.

Foreword by Vaughn Vernon, Series Editor xvii

Foreword by Frank Leymann xxi

Preface xxiii

Part 1: Foundations and Narratives 1

Chapter 1: Application Programming Interface (API) Fundamentals 3

From Local Interfaces to Remote APIs 3

Decision Drivers in API Design 14

A Domain Model for Remote APIs 22

Summary 28

Chapter 2: Lakeside Mutual Case Study 31

Business Context and Requirements 31

Architecture Overview 35

API Design Activities 39

Target API Specification 39

Summary 41

Chapter 3: API Decision Narratives 43

Prelude: Patterns as Decision Options, Forces as Decision Criteria 43

Foundational API Decisions and Patterns 45

Decisions about API Roles and Responsibilities 57

Selecting Message Representation Patterns 70

Interlude: Responsibility and Structure Patterns in the Lakeside Mutual Case 82

Governing API Quality 84

Deciding for API Quality Improvements 98

Decisions about API Evolution 110

Summary 122

Part 2: The Patterns 125

Chapter 4: Pattern Language Introduction 127

Positioning and Scope 128

Patterns: Why and How? 130

Navigating through the Patterns 131

Foundations: API Visibility and Integration Types 137

Basic Structure Patterns 146

Summary 158

Chapter 5: Define Endpoint Types and Operations 161

Introduction to API Roles and Responsibilities 162

Endpoint Roles (aka Service Granularity) 167

Operation Responsibilities 215

Summary 248

Chapter 6: Design Request and Response Message Representations 253

Introduction to Message Representation Design 253

Element Stereotypes 256

Special-Purpose Representations 282

Summary 305

Chapter 7: Refine Message Design for Quality 309

Introduction to API Quality 309

Message Granularity 313

Client-Driven Message Content (aka Response Shaping) 325

Message Exchange Optimization (aka Conversation Efficiency) 344

Summary 355

Chapter 8: Evolve APIs 357

Introduction to API Evolution 357

Versioning and Compatibility Management 362

Life-Cycle Management Guarantees 374

Summary 393

Chapter 9: Document and Communicate API Contracts 395

Introduction to API Documentation 395

Documentation Patterns 398

Summary 421

Part 3: Our Patterns in Action (Now and Then) 423

Chapter 10: Real-World Pattern Stories 425

Large-Scale Process Integration in the Swiss Mortgage Business 426

Offering and Ordering Processes in Building Construction 438

Summary 445

Chapter 11: Conclusion 447

Short Retrospective 448

API Research: Refactoring to Patterns, MDSL, and More 449

The Future of APIs 450

Additional Resources 451

Final Remarks 451

Appendix A: Endpoint Identification and Pattern Selection Guides 453

Appendix B: Implementation of the Lakeside Mutual Case 463

Appendix C: Microservice Domain-Specific Language (MDSL) 471

Bibliography 483

Index 499