Acknowledgements xxiii

1. Introduction 1

References / 6

2. Middleware 7

2.1 Enterprise Information Systems / 7

2.2 Communication / 12

2.3 System and Failure Models / 21

2.4 Remote Procedure Call / 34

2.5 Message-Oriented Middleware / 42

2.6 Web Services and Service-Oriented Architecture (SOA) / 46

2.7 Cloud Computing / 52

2.8 Naming and Discovery / 55

2.9 Further Reading / 56

References / 57

3. Data Modeling 59

3.1 Entities and Relationships / 60

3.1.1 Concepts and Entities / 60

3.1.2 Attributes and Relationships / 61

3.1.3 Properties of Relationship Types / 65

3.1.4 Special Relationship Types / 69

3.2 XML Schemas / 74

3.3 Defining New Types / 79

3.3.1 Defining Simple Types / 79

3.3.2 Defining Complex Types / 82

3.4 Derived Types / 85

3.4.1 Derived Simple Types / 86

3.4.2 Derived Complex Types / 87

3.5 Document Hierarchies / 94

3.6 Relationship Types in XML Schemas / 98

3.7 Metaschemas and Metamodels / 100

3.8 Further Reading / 102

References / 102

4. Data Processing 104

4.1 Processing XML Data / 104

4.1.1 Tree Processing / 105

4.1.2 Schema Binding / 109

4.1.3 Stream Processing / 114

4.1.4 External Processing / 119

4.2 Query Languages and XQuery / 122

4.3 XML Databases / 134

4.3.1 Storage as Relational Tables / 135

4.3.2 Storage as Large Strings / 137

4.3.3 Native XML Storage / 137

4.4 Web Services / 138

4.4.1 SOAP: (not so) Simple Object Access Protocol / 139

4.4.2 WSDL: Web Services Description Language / 145

4.4.3 Web Service Policy / 155

4.5 Presentation Layer: JSON and JQUERY / 159

References / 166

5. Domain-Driven Architecture 167

5.1 Software Architecture / 167

5.2 Domain-Driven Design / 168

5.3 Application Frameworks / 175

5.4 Domain-Specific Languages (DSLs) / 180

5.5 An Example API for Persistent Domain Objects / 188

5.6 Domain-Driven Architecture / 197

5.7 Further Reading / 205

References / 205

6. Service-Oriented Architecture 207

6.1 Services and Procedures / 207

6.2 Service-Oriented Architecture (SOA) / 211

6.3 Service Design Principles / 216

6.4 Service-Oriented Architecture (SOA) Governance / 218

6.5 Standardized Service Contract / 221

6.5.1 Operations Contract / 222

6.5.2 Data Contract / 223

6.5.3 Policy Contract / 224

6.5.4 Binding Contract / 226

6.5.5 Contract Versioning / 231

6.6 Service Loose Coupling / 237

6.6.1 Motivation for Loose Coupling / 237

6.6.2 Contract Development / 239

6.6.3 Loose Coupling Patterns / 242

6.6.4 Cost of Loose Coupling / 246

6.7 Service Abstraction / 248

6.7.1 Platform Abstraction / 248

6.7.2 Protocol Abstraction / 249

6.7.3 Procedural Abstraction / 261

6.7.4 State Abstraction / 264

6.7.5 Data Abstraction / 269

6.7.6 Endpoint Abstraction / 278

6.8 Service Reusability / 278

6.8.1 Parameterization and Bounded Polymorphism / 279

6.8.2 Subtyping, Inheritance, and Contracts / 284

6.8.3 Does Service-Oriented Architecture Require Subtyping? / 289

6.8.4 Patterns for Service Reusability / 292

6.9 Service Autonomy / 299

6.9.1 Replicating Computation / 300

6.9.2 Replicating State / 303

6.9.3 Sources of Errors and Rejuvenation / 308

6.9.4 Caching / 313

6.10 Service Statelessness / 323

6.10.1 Contexts and Dependency Injection / 331

6.11 Service Discoverability / 336

6.11.1 Global Discovery / 336

6.11.2 Local Discovery / 337

6.11.3 Layered Naming / 347

6.12 Further Patterns / 351

6.13 Further Reading / 352

References / 352

7. Resource-Oriented Architecture 359

7.1 Representational State Transfer / 359

7.2 RESTful Web Services / 369

7.3 Resource-Oriented Architecture (ROA) / 379

7.4 Interface Description Languages / 387

7.4.1 Web Services Description Language (WSDL) / 387

7.4.2 Web Application Description Language (WADL) / 390

7.5 An Example Application Program Interface (API) for Resource-Oriented Web Services / 396

7.6 Hypermedia Control and Contract Conformance / 406

7.7 Concluding Remarks / 412

7.8 Further Reading / 414

References / 414

Appendix A: Introduction to Haskell 416

A.1 Types and Functions / 416

A.2 Type Classes and Functors / 425

A.3 Monads / 431

A.4 Further Reading / 436

References / 436

Appendix B: Time in Distributed Systems 437

B.1 What Time Is It? / 437

B.2 Time and Causality / 443

B.3 Applications of Logical and Vector Time / 450

B.3.1 Mutual Exclusion / 450

B.3.2 Quorum Consensus / 451

B.3.3 Distributed Logging / 456

B.3.4 Causal Message Delivery / 458

B.3.5 Distributed Snapshots / 463

B.4 Virtual Time / 468

B.5 Further Reading / 470

References / 470

Index 473

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