Patterns for API Design: Simplifying Integration with Loosely Coupled Message Exchanges

Olaf Zimmermann, Mirko Stocker  
Total pages
November 2022

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Patterns for API Design: Simplifying Integration with Loosely Coupled Message Exchanges

Table of Contents

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


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 Lübke 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 Università 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.