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COM and CORBA Side by Side: Architectures, Strategies, and Implementations

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COM and CORBA Side by Side: Architectures, Strategies, and Implementations


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  • Copyright 1999
  • Dimensions: 7-3/8" x 9-1/4"
  • Pages: 464
  • Edition: 1st
  • Book
  • ISBN-10: 0-201-37945-7
  • ISBN-13: 978-0-201-37945-7

The COM and CORBA technologies are often pitted against each other, viewed simply as competing architectures for creating distributed solutions. While the most significant difference between COM and CORBA is their support for different operating system platforms, software developers must realize that each technology has its own strengths that clearly differentiate it from the other. In COM and CORBA(r) Side by Side, Jason Pritchard objectively describes when and how developers should use both technologies--together or separately--to maximize the success of their designs.

This book helps software practitioners analyze and transcend their personal biases toward COM or CORBA so that they may objectively seek the best implementation strategy. The author helps you cut through vendor marketing hype by presenting a clear, logical formula to help you choose between the two technologies. In short, COM and CORBA(r) Side by Side is an invaluable resource for making informed, critical decisions about using one or both of these technologies in your next project.

Other highlights of this book.

  • Explains why COM and CORBA currently hold dominant positions in the marketplace
  • Describes an objective strategy for assessing the use of the two architectures on the server
  • Examines client approaches for each technology, including design issues related to remoting and security
  • Illustrates how COM and CORBA can be used together, with details on both custom and commercial bridging approaches



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Sample Content

Table of Contents

(Most chapters conclude with "Summary".)


1. The Arrival of Distributed Objects.

Client/Server Beginnings.

2-Tier, 3-Tier, and N-Tier Architectures.

Communicating Between Tiers.

The Power of Distributed Objects.

From Objects to Components.

Managing Distributed Systems.

The State of Distributed Objects.

2. The Dominance of COM and CORBA.

The Distributed Object Landscape.

Microsoft's COM/DCOM.



Java RMI.

ObjectSpace's Voyager.


COM: The Dominant Component Architecture.

CORBA: The Dominant Remoting Architecture.

Evolutionary Trends.

A Test of Wills.

Vendor Perspective.

User Perspective.

Who Is the Winner.

3. Distributed Object Fundamentals.

An Overview of the Fundamentals.

A Distributed Object Example.

COM Object and Clients.

CORBA Object and Clients.

Reviewing the Requirements.

Demonstrating the Fundamentals.

Selecting Data Types.

Defining the Interfaces.

COM IDL and Type Libraries.


Proxies, Stubs, and Skeletons.

COM Proxies and Stubs.

COM Type Library Marshaling.

CORBA Stubs and Skeletons.

Implementing the Servers.

Implementing the Clients.

Using IDL in the COM C++ Client.

Using a Type Library in the COM Visual Basic Client.

Using IDL in the Orbix CORBA C++ Client.

Using IDL in the VisiBroker CORBA Java Client.

Client Implementation.


Object Handles.

COM Interface Pointers in C++.

COM Interface Pointers in Visual Basic.

CORBA Object References in C++.

CORBA Object References in Java.

Creating Objects.

COM Factories.

COM Object Creation in C++.

COM Object Creation in Visual Basic.

CORBA Factories.

CORBA Object Creation in C++ and Java.

Invoking Object Methods.


COM Error Handling in the C++ Client.

COM Error Handling in the Visual Basic Client.

CORBA Exceptions.

CORBA Exception Handling in the C++ and Java Clients.

Destroying Objects.

Destroying COM Objects.

Destroying CORBA Objects.



4. Assessing the Server Side.

What Constitutes the Server Side.

Partitioning the Enterprise.

Strategic Directions of COM and CORBA.

COM: A Vertical Strategy.

CORBA: A Horizontal Strategy.

The Need for an Assessment Strategy.

Assessment Criteria.

Platform Criteria.

Essential Services.


An Assessment Strategy.


Recording the Assessment History.

Rating the Criteria.

Assessment Steps.

An Assessment Example.

COM and CORBA in Your Enterprise Solution.

5. The Server Platform.

Review of the Platform Criteria.

Legacy System Support.

General Approaches for Supporting Legacy Systems.

Identifying Significant Legacy Systems.

Selecting Platforms for New Development.

Wrapper Approach.

Gateway Approach.

Legacy Support When Using COM.

COM and the Wrapper Approach.

COM and the Gateway Approach.

Using COM to Access Legacy Data.

COM Integration with CICS and IMS.

COM Integration with IBM's MQSeries.

Summary of COM-Related Legacy Support.

Legacy Support When Using CORBA.

CORBA and the Wrapper Approach.

CORBA and the Gateway Approach.

Summary of CORBA-Related Legacy Support.

The Development Platform.

COM Development Platforms.

COM/Windows/C++ Development Platform.

COM/Windows/Java Development Platform.

COM/Windows/Visual Basic Development Platform.

Non-Windows COM Development Platforms.

CORBA Development Platforms.

Availability of Development Tools.

COM Development Tools.

CORBA Development Tools.


6. Essential Services.

Review of the Service Criteria.

Distributed Transaction Support.

A Scenario for a Distributed Object Transaction.

COM, MTS, and the Distributed Transaction Coordinator.

CORBA and the Object Transaction Service.

Distributed Security.

DCOM Security.

MTS Security.

CORBA and the Secure Sockets Layer.

The CORBA Security Service.

Messaging Support.

COM and Microsoft Message Queue Server.

CORBA and Messaging Support.

Distributed Object Management.

The Need for Stateless Objects.

COM Object Management Under Microsoft's MTS.

CORBA Object Management Under BEA Systems' M3.


7. Server-Side Intangibles.

Vendor Perception.

Vendor Commitment and Viability.

Vendor Lock-in.

Availability of Product.

Availability of Development Staff.

Product Cost.

Server-Side Summary.


8. The Desktop Client.

Impact of Distributed Objects.

Dominance of COM on the Desktop.

COM Client Approaches.

Custom Interfaces.

Automation Interfaces.

Dual Interfaces.

Installing Remote COM Clients.

COM Development Environments.

The Visual Basic COM Client.

The Visual J++ COM Client.

The Visual C++ COM Client.


9. The Internet Client.

Distributed Object Internet Strategies.

COM Internet Strategies.

CORBA Internet Strategies.

Using COM with Active Server Pages.

Using CORBA in a Java Applet.

The Push Technology Alternative.


10. Client Design Considerations.

Remoting Requirements and Design Issues.

Client Needs Versus Remoting Requirements.

Security Issues for Internet Clients.

Security Issues When Using Active Server Pages.

Security Issues When Using Java Applets.

Migrating from the Desktop to the Internet.

Implementing the COM and CORBA Customer Servers.

The COM Customer Server and Proxy.

The COM Customer Wrapper.

The CORBA Customer Server and Proxy.

Implementing the COM/CORBA Customer Bridge.

The COM-to-CORBA Customer Bridge.

The CORBA-to-COM Customer Bridge.

Implementing the COM and CORBA Customer Clients.

The Visual Basic Customer Client.

The Active Server Pages Customer Client.

The CORBA/Java Customer Client.

Migration Summary.

Client-Side Summary.


11. Custom Bridging Approaches.

Overview of Bridging Example.

Using C++ to Bridge COM and CORBA.

Using Microsoft's JVM as a Bridge.

Using a CORBA/Java ORB with Microsoft's JVM.

A COM-to-CORBA Bridge.

A Visual Basic Client.

Other COM/CORBA Bridging Approaches.

Using COM in Non-Microsoft JVMs.

Bridging ActiveX and JavaBeans.

Using Environments That Support COM and CORBA.

Future Java/COM Support from Microsoft.


12. Commercial Bridging Approach.

COM/CORBA Interworking Specification.

Vendor Support for COM/CORBA Bridging.

A Commercial Bridging Example.

Selecting a Commercial Bridging Product.

The CORBA Server.

Creating a COM View for the CORBA Server.

Using the CORBA Server from a Visual Basic Client.

Using COM Servers from CORBA Clients.

Bridging COM/CORBA Services.


13. Enterprise Application Servers.

Emergence of Enterprise Application Servers.

Early Web Application Servers.

The Need for Enterprise Application Servers.

Enterprise Application Server Criteria.

Enterprise Application Server Approaches.

COM Approach.

CORBA Approach.

Enterprise JavaBeans Approach.


14. Conclusion.

A Summary of What We've Covered.

Embracing COM and CORBA (Part I).

COM and CORBA on the Server (Part II).

COM and CORBA on the Client (Part III).

Bridging COM and CORBA (Part IV).



Appendix A. References.



On COM/CORBA Bridging.

Appendix B. Examples Available for Download.

Chapter 3 Examples.


COM C++ Client.

COM Visual Basic Client.

CORBA C++ Client.

CORBA Java Client.




COM C++ Server.

CORBA C++ Server.

JWPTOC.fm Page xi Wednesday, May 26, 1999 11:21 PMxii Contents

Chapter 6 Examples.

MTS Example.

MTS Account Server.

MTS Teller Server.

MTS Client.

COM Security.

COM Secure Agent Server.

COM Secure Client.

MTS Secure Account Server.

MTS Secure Client.

MSMQ Example.

MSMQ Market Application.

MSMQ Trader Application.

Chapter 8 Examples.

Automation Interface Approach.

Visual J++ Server.

Visual Basic Client.

Visual C++ Client.

Visual J++ Client.

Custom Interface Approach.

Visual C++ Server.

Visual Basic Client.

Visual C++ Client.

Visual J++ Client.

Dual Interface Approach.

Visual Basic Server.

Visual C++ Server.

Visual J++ Server.

Visual Basic Client.

Visual Basic Automation Client.

Visual C++ Client.

Visual J++ Client.

Chapter 9 Examples.


COM Active Server Pages Client.

CORBA Java Applet.




COM Server.

CORBA Server.

Chapter 10 Examples.


COM Active Server Pages Client.

COM Visual Basic Client.

CORBA Java Applet.




COM Customer Interface.

COM Customer Wrapper.

COM Customer Server.

COM Customer Proxy.

COM-to-CORBA Bridge.

CORBA Customer Server.

CORBA Customer Proxy.

CORBA-to-COM Bridge.

Chapter 11 Examples.



COM Client.

COM-to-CORBA Bridge.

CORBA Server.

Chapter 12 Examples.

Bindings Generated by Commercial Bridging Product.

COM Client.

CORBA Server.

Appendix C. Selected Example Code.

MyCheckingAccount Classes (from Ch. 3).

COM/C++ MyCheckingAccount Class.

COM/Visual Basic MyCheckingAccount Class.

CORBA/C++ MyCheckingAccount Class.

CORBA/Java MyCheckingAccount Class.

MTS Components (from Ch. 6).

Ch6Teller MTS Component.

Ch6Account MTS Component.

MSMQ Applications (from Ch. 6).

Trader MSMQ Application.

Stock Market MSMQ Application.

Index. 0201379457T04062001


Topics Covered in the Preface

  • What Is This Book About?
  • Who Should Read This Book?
  • What Specific Areas Are Covered in This Book?
  • What Are the Prerequisites for This Book?
  • Where Are the On-line Resources?

COM and CORBA are all too often viewed as strictly competing technologies. In many areas, the competitive nature of these two technologies cannot be denied; however, each technology has its own strengths that differentiate it from the other. The most significant difference is the support for various operating system platforms. COM is oriented toward the Windows platform, while CORBA is inherently multiplatform. The operating system platform is an important consideration when determining where each technology should be deployed, but many other variables that factor into a decision regarding the use of COM and/or CORBA.

Determining where to use COM, CORBA, or both is a decision that is often based on emotional rather than on logical reasoning. Due to vendor marketing and the fervor of various technology proponents, emotion often ends up being one of the biggest factors in the selection of a distributed object architecture. I have seen several cases where the correct choice for using COM or CORBA was quite obvious, but where a different choice was made for emotional rather than for logical reasons. An objective strategy for choosing where to use COM and CORBA is badly needed.

The influence of emotion on the decision-making process is not too surprising in any part of the software industry. Software developers tend to be artisans and not engineers. Artisans rely on their instincts and rules of thumb when making critical decisions. Engineers rely on well-defined processes and formulae. While all of us should strive to evolve software development into an engineering discipline, we just arenIt there yet. The processes and formulae usually do not exist for making definitive decisions with regard to software.

Perhaps the greatest difficulty with understanding software technologies, especially technologies like COM and CORBA, is the ever-expanding functionality provided by such technologies. None of us can hope to understand every nuance of COM or CORBA. We must therefore become specialized and focus on very specific areas that meet our current needs. As we become more specialized, we lose sight of the big picture. This has a negative effect on our ability to make rational decisions. To escape specialization, we must rely on other people to make us aware of the key factors that need to be considered when deciding where complex technologies like COM and CORBA should be used.

What Is This Book About?

This book provides a comprehensive comparison of COM and CORBA. It brings together the critical elements that must be considered when deciding where COM and CORBA should be used. This book also discusses various approaches for using COM and CORBA together in situations where the use of both is desired.

Throughout this book, COM and CORBA are compared in a side-by-side manner so that the similarities and differences between COM and CORBA are accentuated. The best way to understand what is meant by the phrase side-by-side is to examine the bookIs table of contents and note that the focus constantly shifts between discussions of COM, CORBA, or both. Within individual sections, comparisons are made between COM and CORBA whenever possible.

While writing this book, I have made every effort to avoid any bias toward either COM or CORBA. This book is definitely not about promoting one technology over the other. I have been fortunate enough to work with COM and CORBA on a multitude of projects, and I very much enjoy using both of them. In this book, I have done my best to objectively present useful information that will be helpful when choosing COM and/or CORBA.

Who Should Read This Book?

Software products based on COM and CORBA will undoubtedly provide the distributed object infrastructures for many future software systems. This book is designed for technical managers and strategists who need to determine where COM and CORBA should be used in their particular organizations. This book will also benefit developers who want to have an impact on such decisions.

This book also allows developers who have a working knowledge of either COM or CORBA to leverage their existing knowledge to better understand both technologies. The side-by-side nature of this book allows developers who are familiar with one approach to easily identify parallels with the other approach. The identification of such parallels provides a powerful mechanism for learning. As a result, a software developer who understands COM can use this book to better understand CORBA; a software developer who understands CORBA can use this book to better understand COM.

What Specific Areas Are Covered in This Book?

This book is divided into four parts that can be read independently of one another. If you are unfamiliar with either COM or CORBA, you should look at Part I first since it provides information on COM and CORBA fundamentals. After completing Part I, the rest of the parts can be read in any order.

Part I, Embracing COM and CORBA. This part of the book provides a brief history leading up to distributed objects and discusses why COM and CORBA currently hold dominant positions in the marketplace. Part I concludes by performing an extensive side-by-side comparison of COM/CORBA technical fundamentals.

Part II, COM and CORBA on the Server. This part of the book discusses the use of COM and CORBA on the server side. It begins by describing an objective strategy for assessing the appropriateness of COM and CORBA for a specific server-side domain. Part II then examines platform issues (including legacy system support), essential services (transactions, security, etc.), and intangibles that must often be considered when choosing between COM and CORBA.

Part III, COM and CORBA on the Client. This part of the book examines client approaches for using COM and CORBA. Because Windows controls the desktop, Part III begins by looking at COM desktop client approaches. It then examines COM/CORBA Internet client approaches and also discusses design issues related to remoting and security. Part III concludes by providing an example that demonstrates a migration path from the desktop to the Internet.

Part IV, Bridging COM and CORBA. This part of the book examines approaches for using COM and CORBA together. It begins by examining custom approaches for bridging COM and CORBA. Part IV then examines commercial bridging approaches based on the OMGIs COM/CORBA interworking architecture. Part IV concludes with a discussion of enterprise application servers based on COM, CORBA, and Enterprise JavaBeans.

What Are the Prerequisites for This Book?

The COM examples presented in this book use C++, Java, and Visual Basic. The CORBA examples use C++ and Java. While some chapters in the book are not code-oriented, you will probably have trouble comprehending this book if you are not proficient in C++ or Java.

If you are planning to use COM or CORBA, you have probably already obtained references that focus directly on COM, CORBA, or COM/CORBA bridging. This book provides a comparison of COM and CORBA and also discusses COM/CORBA bridging. It does not, however, attempt to provide a complete reference for any of these areas. Depending on your needs, you may require books that focus exclusively on COM, CORBA, or COM/CORBA bridging to supplement the material contained in this book. For a list of such books that I have found useful, see the references (Appendix A) at the end of the book.

Where Are the On-line Resources?

The best on-line source for information on COM, including the COM specification, can be found at http://www.microsoft.com/com.

A wealth of information related to CORBA can be found at http://www.omg.org.

Information related to this book, including code examples, can be found at http://www.pobox.com/~pritchard/com_corba.html.

If you still havenIt found what you're looking for and think that I can help, send e-mail to mailto:pritchard@pobox.com.



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