The eagerly awaited Pattern-Oriented Software Architecture
(POSA) Volume 4 is about a pattern language for distributed
computing.

The authors will guide you through the best practices and
introduce you to key areas of building distributed software
systems. POSA 4 connects many stand-alone patterns, pattern
collections and pattern languages from the existing body of
literature found in the POSA series. Such patterns relate to and
are useful for distributed computing to a single language.

* The panel of experts provides you with a consistent and
coherent holistic view on the craft of building distributed
systems.

* Includes a foreword by Martin Fowler

* A must read for practitioners who want practical advice to
develop a comprehensive language integrating patterns from key
literature.

Frank Buschmann, Siemens AG, Germany

Kevlin Henney, Curbralan, Bristol, UK

Douglas C. Schmidt, Vanderbilt University, Nashville, Tennessee, USA

Many patterns in the software literature focus on distributed computing. Until recently, there has been no holistic view of distributed computing that emphasizes how groups of patterns complete and complement each other. Building complex distributed systems has therefore been a craft that many have tried, but few have mastered. The eagerly anticipated Pattern-Oriented Software Architecture (POSA) Volume 4 provides the missing link in the development of software for distributed systems: it provides a holistic view for distributed computing.

Leading experts, Frank Buschmann, Kevlin Henney, and Douglas C. Schmidt describe a pattern language that links hundreds of patterns relevant for distributed computing. The authors guide you through the best practices in key areas of developing software for distributed computing systems. POSA 4 connects many stand-alone patterns, pattern collections, and languages from the existing body of literature found in the POSA series and other respected sources. The authors explain what pattern languages are and how to use them effectively, by comparing various patterns and distributed computing paradigms.

The material covers concepts, which provides the context of the book; a story, which describes how a real-world process control system for warehouse management was designed with the authors' pattern language for distributed computing; and the language itself, which forms the main part of the book. The language addresses technical topics relevant for building distributed systems, such as:

• Object interaction
• Interface and component partitioning
• Application control
• Resource management
• Concurrency and synchronization

POSA 4 is also the only book to offer practical advice demonstrating how to integrate patterns from key literature to provide a comprehensive pattern language for developing distributed computing middleware and applications.

Zusammenfassung
The eagerly awaited Pattern-Oriented Software Architecture (POSA) Volume 4 is about a pattern language for distributed computing.

The authors will guide you through the best practices and introduce you to key areas of building distributed software systems. POSA 4 connects many stand-alone patterns, pattern collections and pattern languages from the existing body of literature found in the POSA series. Such patterns relate to and are useful for distributed computing to a single language.

• The panel of experts provides you with a consistent and coherent holistic view on the craft of building distributed systems.
• Includes a foreword by Martin Fowler
• A must read for practitioners who want practical advice to develop a comprehensive language integrating patterns from key literature.

Foreword xv

About This Book xvii

About The Authors xxiii

Guide To The Reader xxvii

Part I Some Concepts 1

1 On Patterns and Pattern Languages 3

1.1 Patterns Introduced 4

1.2 Inside Patterns 6

1.3 Between Patterns 10

1.4 Into Pattern Languages 13

1.5 Patterns Connected 15

2 On Distributed Systems 17

2.1 Benefits of Distribution 18

2.2 Challenges of Distribution 20

2.3 Technologies for Supporting Distribution 22

2.4 Limitations of Middleware 32

3 On the Pattern Language 33

3.1 Intent, Scope, and Audience 34

3.2 Origins and Genesis 35

3.3 Structure and Content 36

3.4 Presentation 44

3.5 Practical Use 49

Part II A Story 53

4 Warehouse Management Process Control 57

4.1 System Scope 58

4.2 Warehouse Management Process Control 60

5 Baseline Architecture 65

5.1 Architecture Context 66

5.2 Partitioning the Big Ball of Mud 67

5.3 Decomposing the Layers 68

5.4 Accessing Domain Object Functionality 71

5.5 Bridging the Network 72

5.6 Separating User Interfaces 76

5.7 Distributing Functionality 79

5.8 Supporting Concurrent Domain Object Access 82

5.9 Achieving Scalable Concurrency 85

5.10 Crossing the Object-Oriented/Relational Divide 87

5.11 Configuring Domain Objects at Runtime 89

5.12 Baseline Architecture Summary 90

6 Communication Middleware 95

6.1 A Middleware Architecture for Distributed Systems 96

6.2 Structuring the Internal Design of the Middleware 100

6.3 Encapsulating Low-level System Mechanisms 103

6.4 Demultiplexing ORB Core Events 105

6.5 Managing ORB Connections 108

6.6 Enhancing ORB Scalability 111

6.7 Implementing a Synchronized Request Queue 114

6.8 Interchangeable Internal ORB Mechanisms 116

6.9 Consolidating ORB Strategies 118

6.10 Dynamic Configuration of ORBs 121

6.11 Communication Middleware Summary 124

7 Warehouse Topology 129

7.1 Warehouse Topology Baseline 130

7.2 Representing Hierarchical Storage 131

7.3 Navigating the Storage Hierarchy 133

7.4 Modeling Storage Properties 135

7.5 Varying Storage Behavior 137

7.6 Realizing Global Functionality 140

7.7 Traversing the Warehouse Topology 142

7.8 Supporting Control Flow Extensions 144

7.9 Connecting to the Database 146

7.10 Maintaining In-Memory Storage Data 147

7.11 Configuring the Warehouse Topology 149

7.12 Detailing the Explicit Interface 151

7.13 Warehouse Topology Summary 153

8 The Story Behind The Pattern Story 157

Part III The Language 163

9 From Mud To Structure 167

Domain Model ** 182

Layers ** 185

Model-View-Controller ** 188

Presentation-Abstraction-Control 191

Microkernel ** 194

Reflection * 197

Pipes and Filters ** 200

Shared Repository ** 202

Blackboard 205

Domain Object ** 208

10 Distribution Infrastructure 211

Messaging ** 221

Message Channel ** 224

Message Endpoint ** 227

Message Translator ** 229

Message Router ** 231

Publisher-Subscriber ** 234

Broker ** 237

Client Proxy ** 240

Requestor ** 242

Invoker ** 244

Client Request Handler ** 246

Server Request Handler ** 249

11 Event Demultiplexing and Dispatching 253

Reactor ** 259

Proactor * 262

Acceptor-Connector ** 265

Asynchronous Completion Token ** 268

12 Interface Partitioning 271

Explicit Interface ** 281

Extension Interface ** 284

Introspective Interface…