Markus Völter - Remoting Patterns: Foundations of Enterprise, Internet and Realtime Distributed Object Middleware

Remoting Patterns

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Library of Congress Cataloging-in-Publication Data

Vlter, Markus.
Remoting patterns: foundations of enterprise, internet and realtime distributed object middleware / Markus Vlter, Michael Kircher, Uwe Zdun.
p. cm.
Includes bibliographical references and index.
ISBN 0-470-85662-9 (cloth : alk. paper)
1. Computer softwareDevelopment. 2. Software patterns. 3. Electronic data processing Distributed processing. 4. Middleware. I. Kircher, Michael. II. Zdun, Uwe. III. Title.
QA76.76.D47V65 2004
005.1dc22

2004018713

British Library Cataloguing in Publication Data

A catalogue record for this book is available from the British Library

ISBN 0-470-85662-9

Foreword

Many of todays enterprise computing systems are powered by distributed object middleware. Such systems, which are common in industries such as telecommunications, finance, manufacturing, and government, often support applications that are critical to particular business operations. Because of this, distributed object middleware is often held to stringent performance, reliability, and availability requirements. Fortunately, modern approaches have no problem meeting or exceeding these requirements. Today, successful distributed object systems are essentially taken for granted.

There was a time, however, when making such claims about the possibilities of distributed objects would have met with disbelief and derision. In their early days, distributed object approaches were often viewed as mere academic fluff with no practical utility. Fortunately, the creators of visionary distributed objects systems such as Eden, Argus, Emerald, COMANDOS, and others were undeterred by such opinion. Despite the fact that the experimental distributed object systems of the 1980s were generally impractical too big, too slow, or based on features available only from particular specialized platforms or programming languages the exploration and experimentation required to put them together collectively paved the way for the practical distributed objects systems that followed.

The 1990s saw the rise of several commercially successful and popular distributed object approaches, notably the Common Object Request Broker Architecture (CORBA) promoted by the Object Management Group (OMG) and Microsofts Common Object Model (COM). CORBA was specifically designed to address the inherent heterogeneity of business computing networks, where mixtures of machine types, operating systems, programming languages, and application styles are the norm and must co-exist and cooperate. COM, on the other hand, was built specifically to support component-oriented applications running on the Microsoft Windows operating system.

Today, COM has been largely subsumed by its successor, .NET, while CORBA remains in wide use as a well-proven architecture for building and deploying significant enterprise-scale heterogeneous systems, as well as real-time and embedded systems.

As this book so lucidly explains, despite the fact that CORBA and COM were designed for fundamentally different purposes, they share a number of similarities. These similarities range from basic notions, including remote objects, client and server applications, proxies, marshalers, synchronous and asynchronous communications, and interface descriptions, to more advanced areas, including object identification and lookup, infrastructure extension, and lifecycle management. Not surprisingly, though, these similarities do not end at CORBA and COM. They can also be found in newer technologies and approaches, including .NET, the Java 2 Enterprise Edition (J2EE), and even in Web Services (which, strictly speaking, is not a pure distributed object technology, but nevertheless has inherited many of its characteristics).

Such similarities are of course better known as patterns. Patterns are generally not so much created as discovered, much as a miner finds a diamond or a gold nugget buried in the earth. Successful patterns result from the study of successful systems, and the remoting patterns presented here are no exception. Our authors, Markus, Michael, and Uwe, who are each well versed in both the theory and practice of distributed objects, have worked extensively with each of the technologies Ive mentioned. Applying their pattern-mining talents and efforts, they have captured for the rest of us the critical essence of a number of successful solutions and approaches found in a number of similar distributed objects technologies.

Given my own long history with CORBA, I am not surprised to find that several of the patterns that Markus, Michael, and Uwe document here are among my personal favorites. For example, topping my list is the Invocation Interceptor pattern, which I have found to be critical for creating distributed objects middleware that provides extensibility and modularity without sacrificing performance. Another favorite of mine is the Leasing pattern, which can be extremely effective for managing object lifecycles.

This book does not just describe a few remoting patterns, however. While many patterns books comprise only a loose collection of patterns, this book also provides a series of technology projections that tie the patterns directly back to the technologies that employ them. These projections clearly show how the patterns are used within .NET, CORBA, and Web Services, effectively recreating these architectures from the patterns mined from within them. With technology projections like these, it has never been easier to see the relationships and roles of different patterns with respect to each other within an entire architecture. These technology projections clearly link the patterns, which are already invaluable by themselves, into a comprehensive, harmonious, and rich distributed objects pattern language. In doing so, they conspicuously reveal the similarities among these different distributed object technologies. Indeed, we might have avoided the overzealous and tiresome CORBA vs. COM arguments of the mid-1990s had we had these technology projections and patterns at the time.