SOA with REST

Service-Related Granularity 45 Service Profiles 46 SOA Design Patterns 46 4.2 Further Reading 49 4.3 Case Study Example 50 Chapter 5: REST Constraints and Goals 51 5.1 REST Constraints 52 Client-Server 53 Stateless 54 Cache 55 Interface/Uniform Contract 55 Layered System 56 Code-On-Demand 57 5.2 Goals of the REST Architectural Style 58 Performance 58 Scalability 59 Simplicity 60 Modifiability 61 Visibility 61 Portability 62 Reliability 62 Case Study Example 63 Part II: RESTful Service-Orientation Chapter 6: Service Contracts with REST 67 6.1 Uniform Contract Elements 68 Resource Identifier Syntax (and Resources) 69 URIs (and URLs and URNs) 69 Resource Identifiers and REST Services 71 Methods 71 Media Types 73 6.2 REST Service Capabilities and REST Service Contracts 75 6.3 REST Service Contracts vs. Non-REST Service Contracts 77 Non-REST Service with Custom Service Contract 77 REST Service with Uniform Contract 79 HTTP Messaging vs. SOAP Messaging 81 REST Service Contracts with WSDL? 82 6.4 The Role of Hypermedia 83 URI Templates and Resource Queries 86 6.5 REST Service Contracts and Late Binding 87 Case Study Example 90 Chapter 7: Service-Orientation with REST 93 7.1 "SOA vs. REST" or "SOA + REST"? 95 7.2 Design Goals 97 Increased Intrinsic Interoperability 97 Increased Federation 98 Increased Vendor Diversity Options 99 Increased Business and Technology Alignment 100 Increased ROI 100 Increased Organizational Agility 102 Reduced IT Burden 102 Common Goals 103 7.3 Design Principles and Constraints 104 Standardized Service Contract 104 Service Loose Coupling 105 Service Abstraction 107 Service Reusability 109 Service Autonomy 110 Service Statelessness 111 Service Discoverability 113 Service Composability 114 Common Conflicts 114 Stateful Interactions 115 Service-Specific Contract Details 115 Case Study Example 116 Part III: Service-Oriented Analysis and Design with REST Chapter 8: Mainstream SOA Methodology and REST 127 8.1 Service Inventory Analysis 131 8.2 Service-Oriented Analysis (Service Modeling) 133 8.3 Service-Oriented Design (Service Contract) 135 8.4 Service Logic Design 137 8.5 Service Discovery 137 8.6 Service Versioning and Retirement 138 Chapter 9: Analysis and Service Modeling with REST 139 9.1 Uniform Contract Modeling and REST Service Inventory Modeling 141 REST Constraints and Uniform Contract Modeling 144 REST Service Centralization and Normalization 146 9.2 REST Service Modeling 147 REST Service Capability Granularity 148 Resources vs. Entities 149 REST Service Modeling Process 150 Case Study Example 152 Step 1: Decompose Business Process (into Granular Actions) 152 Case Study Example 152 Step 2: Filter Out Unsuitable Actions 154 Case Study Example 154 Step 3: Identify Agnostic Service Candidates 155 Case Study Example 157 Event Service Candidate (Entity) 157 Award Service Candidate (Entity) 158 Student Service Candidate (Entity) 158 Notification Service Candidate (Utility) 159 Document Service Candidate (Utility) 159 Step 4: Identify Process-Specific Logic 160 Case Study Example 160 Confer Student Award Service Candidate (Task) 161 Step 5: Identify Resources 161 Case Study Example 162 Step 6: Associate Service Capabilities with Resources and Methods 163 Case Study Example 164 Confer Student Award Service Candidate (Task) 164 Event Service Candidate (Entity) 164 Award Service Candidate (Entity) 165 Student Service Candidate (Entity) 165 Notification Service Candidate (Utility) 166 Document Service Candidate (Utility) 166 Step 7: Apply Service-Orientation 167 Case Study Example 167 Step 8: Identify Candidate Service Compositions 167 Case Study Example 168 Step 9: Analyze Processing Requirements 169 Step 10: Define Utility Service Candidates 170 Step 11: Associate Utility-Centric Service Capabilities with Resources and Methods 171 Step 12: Apply Service-Orientation 171 Step 13: Revise Candidate Service Compositions 171 Step 14: Revise Resource Definitions 171 Step 15: Revise Capability Candidate Grouping 172 Additional Considerations 172 Chapter 10: Service-Oriented Design with REST 173 10.1 Uniform Contract Design Considerations 175 Designing and Standardizing Methods 175 Designing and Standardizing HTTP Headers 177 Designing and Standardizing HTTP Response Codes 179 Customizing Response Codes 184 Designing Media Types 186 Designing Schemas for Media Types 188 Service-Specific XML Schemas 189 10.2 REST Service Contract Design 191 Designing Services Based on Service Models 191 Task Services 191 Entity Services 192 Utility Services 193 Designing and Standardizing Resource Identifiers 194 Service Names in Resource Identifiers 195 Other URI Components 196 Resource Identifier Overlap 197 Resource Identifier Design Guidelines 199 Designing with and Standardizing REST Constraints 201 Stateless 201 Cache 202 Uniform Contract 203 Layered System 204 Case Study Example 205 Confer Student Award Service Contract (Task) 205 Event Service Contract (Entity) 207 Award Service Contract (Entity) 207 Student Transcript Service Contract (Entity) 208 Notification and Document Service Contracts (Utility) 209 10.3 Complex Method Design 211 Stateless Complex Methods 214 Fetch Method 214 Store Method 215 Delta Method 217 Async Method 219 Stateful Complex Methods 221 Trans Method 221 PubSub Method 222 Case Study Example 224 OptLock Complex Method 224 PesLock Complex Method 226 Part IV: Service Composition with REST Chapter 11: Fundamental Service Composition with REST 231 11.1 Service Composition Terminology 233 Compositions and Composition Instances 233 Composition Members and Controllers 234 Service Compositions Are Actually Service Capability Compositions 235 Designated Controllers 236 Collective Composability 236 Service Activities 238 Composition Initiators 239 Point-to-Point Data Exchanges and Compositions 240 11.2 Service Composition Design Influences 241 Service-Orientation Principles and Composition Design 241 Standardized Service Contract and the Uniform Contract 242 Service Loose Coupling and the Uniform Contract 243 Service Abstraction and Composition Information Hiding 244 Service Reusability for Repeatable Composition 245 Service Autonomy and Composition Autonomy Loss 245 Service Statelessness and Stateless 246 Service Composability and Service-Orientation 246 REST Constraints and Composition Design 247 Stateless and Stateful Compositions 247 Cache and Layered System 248 Code-on-Demand and Composition Logic Deferral 248 Uniform Contract and Composition Coupling 248 11.3 Composition Hierarchies and Layers 249 Task Services Composing Entity Services 250 Entity Services Composing Entity Services 251 11.4 REST Service Composition Design Considerations 253 Synchronous and Asynchronous Service Compositions 253 Idempotent Service Activities 254 Lingering Composition State 255 Binding Between Composition Participants 255 11.5 A Step-by-Step Service Activity 258 1. Request to Purchase a Ticket 258 2. Verify the Requested Flight Details 258 3. Confirm a Seat on the Flight 259 4. Generate an Invoice 259 5. Create the Ticket 260 Summary 260 Chapter 12: Advanced Service Composition with REST 261 12.1 Service Compositions and Stateless 263 Composition Design with Service Statelessness 264 Composition Design with Stateless 265 12.2 Cross-Service Transactions with REST 266 REST-Friendly Atomic Service Transactions 267 Phase 1: Initialize 267 Phase 2: Reserve 268 Phase 3A: Confirm 269 Phase 3B: Cancel 269 Phase 3C: Timeout 270 Compliance with Stateless 271 Additional Considerations 272 REST-Friendly Compensating Service Transactions 272 Phase 1: Begin 273 Phase 2: Do 273 Phase 3A: Complete 274 Phase 3B: Undo 274 Phase 3C: Timeout 275 Compliance with Stateless 276 Additional Considerations 276 Non-REST-Friendly Atomic Service Transactions 276 Phase 1: Initialize 277 Phase 2: Do 277 Phase 3: Prepare 278 Phase 4A: Commit 279 Phase 4B: Rollback 279 Phase 4C: Timeout 280 Compliance with Stateless 280 Additional Considerations 281 12.3 Event-Driven Interactions with REST 282 Event-Driven Messaging 282 Compliance with Stateless 283 Message Polling 285 Compliance with Stateless 287 12.4 Service Composition with Dynamic Binding and Logic Deferral 288 Denormalized Capabilities Across Normalized Services 289 Composition Deepening 292 Dynamically Binding with Common Properties 294 Runtime Logic Deferral 297 12.5 Service Composition Across Service Inventories 299 Inventory Endpoint with REST 299 Dynamic Binding Between Service Inventories with Baseline Standardization 302 Chapter 13: Service Composition with REST Case Study 305 13.1 Revisiting the Confer Student Award Process 306 13.2 Application Submission and Task Service Invocation 310 13.3 Confer Student Award Service Composition Instance (Pre-Review Service Activity View) 312 Step 1: Composition Initiator to Confer Student Award Task Service (A) 312 Step 2: Confer Student Award Task Service to Event Entity Service (B) 312 Step 3: Event Entity Service to Confer Student Award Task Service (B) 313 Step 4: Confer Student Award Task Service to Award Entity Service (E) 314 Step 5: Award Entity Service to Confer Student Award Task Service (E) 314 Step 6: Confer Student Award Task Service to Award Entity Service (E) 314 Step 7: Award Entity Service to Confer Student Award Task Service (E) 315 Step 8: Confer Student Award Task Service to Student Entity Service (F) 315 Step 9: Student Entity Service to Confer Student Award Task Service (F) 315 Step 10: Confer Student Award Task Service to Student Transcript Entity Service (F) 316 Step 11: Student Transcript Entity Service to Confer Student Award Task Service (F) 316 Step 12: Confer Student Award Task Service to Composition Initiator 316 13.4 Review of Pending Applications and Task Service Invocation 317 Confer Student Award Service Composition Instance (Post-Review Service Activity View) 318 Step 1: Composition Initiator to Confer Student Award Task Service (L) 320 Step 2: Confer Student Award Task Service to Notification Utility Service (N) 320 Step 3: Notification Utility Service to Student Entity Service (N) 320 Step 4: Student Entity Service to Notification Utility Service (N) 320 Step 5: Notification Utility Service to Confer Student Award Task Service (N) 321 Intermediate Step: Confer Student Award Task Service to Transaction Coordinator (P, Q) 321 Intermediate Step: Transaction Coordinator to Confer Student Award Task Service (P, Q) 321 Step 6: Confer Student Award Task Service to Conferral Entity Service (P) 322 Intermediate Step: Conferral Entity Service to Transaction Coordinator (P) 322 Intermediate Step: Transaction Coordinator to Conferral Entity Service 322 Step 7: Conferral Entity Service to Confer Student Award Task Service (Q) 322 Step 8: Confer Student Award Task Service to Student Manuscript Entity Service (Q) 323 Intermediate Step: Student Transcript Entity Service to Transaction Controller (Q) 323 Intermediate Step: Transaction Controller to Student Transcript Entity Service (Q) 323 Step 9: Student Transcript Entity Service to Confer Student Award Task Service (Q) 324 Intermediate Step: Confer Student Award Task Service to Transaction Coordinator (P, Q) 324 Intermediate Step: Transaction Coordinator to Confer Student Award Task Service (P, Q) 324 Step 10: Confer Student Award Task Service to Composition Initiator 324 Part V: Supplemental Chapter 14: Design Patterns for SOA with REST 327 14.1 REST-Inspired SOA Design Patterns 329 Content Negotiation 331 Related Patterns 332 Related Service-Oriented Computing Goals 332 Endpoint Redirection 332 Related Patterns 333 Related Service-Oriented Computing Goals 333 Entity Linking 333 Related Patterns 335 Related Service-Oriented Computing Goals 335 Idempotent Capability 335 Related Patterns 335 Related Service-Oriented Computing Goals 335 Lightweight Endpoint 336 Related Patterns 337 Related Service-Oriented Computing Goals 337 Reusable Contract 338 Related Patterns 338 Related Service-Oriented Computing Goals 339 Uniform Contract 339 14.2 Other Relevant SOA Design Patterns 340 Contract Centralization 340 Contract Denormalization 340 Domain Inventory 340 Schema Centralization 341 State Messaging 341 Validation Abstraction 342 Chapter 15: Service Versioning with REST 343 15.1 Versioning Basics 346 REST Service Contract Compatibility 346 Compatible and Incompatible Changes 348 Uniform Contract Method Compatibility 349 Uniform Contract Media Type Compatibility 350 Media Types and Forwards-compatibility 354 15.2 Version Identifiers 355 Using Version Identifiers 356 Version Identifiers and the Uniform Contract 358 Chapter 16: Uniform Contract Profiles 361 16.1 Uniform Contract Profile Template 362 Uniform-Level Structure 363 Method Profile Structure 364 Media Type Profile Structure 365 16.2 REST Service Profile Considerations 367 16.3 Case Study Example 369 Uniform-Level Structure: MUAUC 370 Method Profile Structure: Fetch 371 Response Code Handling for GET Methods in Fetch Method 373 Method Profile Structure: Store 374 Response Code Handling for PUT and DELETE Methods in Store Method 376 Method Profile Structure: GET 377 Method Profile Structure: PUT 378 Media Type Profile Structure: Invoice (application/vnd.edu.mua.invoice+xml) 379 Part VI: Appendices Appendix A: Case Study Conclusion 383 Appendix B: Industry Standards Supporting the Web 387 The Internet Engineering Taskforce (IETF) 388 The World Wide Web Consortium 389 Other Web Standards 390 Appendix C: REST Constraints Reference 391 Appendix D: Service-Orientation Principles Reference 409 Appendix E: SOA Design Patterns Reference 425 Appendix F: State Concepts and Types 521 State Management Explained 522 State Management in Abstract 522 Origins of State Management 523 Deferral vs. Delegation 527 Types of State 527 Active and Passive 527 Stateless and Stateful 528 Session and Context Data 528 Measuring Service Statelessness 530 Appendix G: The Annotated SOA Manifesto 533 Appendix H: Additional Resources 547 www.whatisrest.com 548 Bibliography and References 548 Resources 551 www.servicetechbooks.com 551 www.soaschool.com, www.cloudschool.com 551 www.servicetechmag.com 552 www.soaglossary.com 552 www.servicetechspecs.com 552 www.soapatterns.org, www.cloudpatterns.org 552 www.serviceorientation.com, www.soaprinciples.com, www.whatissoa.com 552 www.servicetechsymposium.com 552 About the Authors 553 About the Pattern Co-Contributors 555 About the Foreword Contributor 557 Index 559

and practice of REST and related styles as well as broader software and systems architecture topics. Cesare Pautasso is an assistant professor at the Faculty of Informatics at the University of Lugano, Switzerland. Previously he was a researcher at the IBM Zurich Research Lab and a senior researcher at ETH Zurich, where he also completed his graduate studies with a Ph.D. in 2004. His teaching, research, and consulting activities both in academia and in industry cover advanced topics related to Software Architecture, Service Oriented Computing, and emerging RESTful Web services technologies. His research group focuses on building experimental systems to explore the intersection between the REST architectural style and model-driven software composition techniques, business process management, and liquid, self-organizing service-oriented architectures. He is an active member of IEEE and ACM, where he has participated in more than 100 international conference/workshop program committees. He has started the series of International Workshops on RESTful Design (WS-REST) at the WWW conference and was the general chair of the 9th IEEE European Conference on Web Services (ECOWS 2011). He regularly referees for Swiss, EU, and international funding agencies. Raj Balasubramanian is a senior technologist from the Business Process Optimization (BPO) team within IBM Software Group focused on delivering SOA/BPM/Cloud solution across industries. Depending on the needs of the customer he has played the role of an enterprise architect, system architect, or solution architect to deliver on the engagement at hand. Prior to the focus on BPO, he was a lead portal architect delivering portal solutions to medium and large enterprise as part of the Lotus brand. He has published numerous articles on IBM DeveloperWorks and speaks at industry conferences on a variety of topics. His interests are in distributed systems, applying Web constructs to solution design, and using formal models and analytics to reason about large systems. Raj is also pursuing a Ph.D. in ECE at University of Texas at Austin where he is applying machine learning and data mining techniques to networked data from social Web to human travel. His official profile is on http://raj.balasubramanians.com, which links to his various personas.

opportunities arise for service composition architecture designs. A comprehensive guide and a must-read for any serious IT architect considering REST-style services for application architectures." --Roger Stoffers, Solution Architect, Hewlett Packard "Service-orientation and REST both are architectural styles that are cornerstones of modern applications and cloud computing. Both aim to deliver scalable, interoperable solutions, but their different roots don't always make them a natural fit. SOA with REST explains how the two styles can work together in enterprise environments. It discusses a design process for a services portfolio that meets the goals of SOA and at the same time designs services that comply with the established REST constraints. It also shows pragmatic approaches to meet enterprise-grade requirements with the REST programming style but relaxes constraints where necessary." --Christoph Schittko, Director of Cloud Strategy, Microsoft "An inspirational book that provides deep insight into the design and development of next-generation service-oriented systems based on the use of REST. This book clarifies the convergence of SOA and REST with no-nonsense content that addresses common questions and issues head-on. An essential 'instrument of modern service implementation' and a powerful body of knowledge for software designers, architects, and consultants." --Pethuru Raj, Ph.D., Enterprise Architecture (EA) Consultant, Wipro Consulting Services "The Service Technology Series from Thomas Erl continues its tradition of using simple examples to elucidate complicated concepts. With the latest in the series, SOA with REST, the authors have created a resource that discusses REST through the lenses of the common SOA pattern language. SOA with REST is a fantastic resource for the enterprise architect and developer alike!" --Kevin P. Davis, Ph.D., Software Architect "Unlike many other texts on the subject, SOA with REST is a well-rounded, easy-to-read narrative, including real-world case studies that appeal to both developers and analysts. This makes it an indispensable source for any SOA practitioner or any professional who is planning to initiate an SOA project." --Theodore T. Morrison, Certified SOA Analyst, CSM, Geocent, LLC "The book is a must-read for any IT architect or software engineer who wants to gain a deep understanding of the principles, patterns, and implementation concepts that pertain to building REST-based applications for service-oriented architectures. It goes well beyond fundamental topics to explore the relationship between REST and various specific SOA principles and patterns." --Sanjay Singh, Certified SOA Architect, Development Manager, NorthgateArinso "An authoritative, well-written reference for enterprise architects, analysts, developers, and others. This book shows not only the elegance, simplicity, and versatility of REST, it also gives us a clear understanding of how REST synergizes with SOA and service-orientation, how REST can impact SOA design goals, how we can design and develop REST services, and how we can address the unique challenges of integrating RESTfulness into service-orientation. This book is required reading for anyone who desires technical mastery of building service-oriented architectures with REST." --Philip Wik, MSS Technology "This is a comprehensive and fundamental book to understand how to employ REST in service-oriented architectures. The many examples provided and the patterns described will be an invaluable help to any practitioner interested in service orientation." --Gustavo Alonso, Department of Computer Science, ETH Zurich "SOA and REST are two very important architectural styles for distributed computing. SOA is successfully adopted by most enterprises, and the REST style is getting more attention from both researcher and industry users. The book SOA with REST introduces a new architectural style that is ingeniously combining both SOA and REST styles and clearly reveals how SOA and REST can work together to generate successful enterprise SOA strategies with REST, along with guidance for making architecture design decisions. This book is a bible of best practices for designing and implementing SOA architecture with REST. It is a must-have reference book for both IT practitioners and researchers." --Longji Tang, FedEx IT Senior Technical Advisor, Ph.D. in CSSE "REST and SOA are two of the most misunderstood terms in the software industry over the past decade. Yet the REST architectural style coupled with modern RESTful framework implementations provides a scalable and reliable approach to SOA. This book covers all you need to know about how to take the principles of REST and apply them in small and large SOA developments. If you are familiar with REST and thinking about SOA, then you need this book. If you have not considered REST in your SOA work, then this book is for you, too. Covering concepts of both REST and SOA, as well as design patterns and when to use them, the book is a wonderful companion and a good tool for architects and engineers." --Dr. Mark Little, CTO JBoss, Red Hat "This book is an excellent introduction into how SOA methodology can be used with services implementing a RESTful architectural style. Thomas Erl and his co-authors help SOA architects to better understand the implications of utilizing and the requirements for integrating REST into the service-oriented architecting process." --Gerald Beuchelt, MITRE