COM+ Programming with Visual Basic

How This Book Is Organized

The term COM+ is a marketing term and, as such, tends to confuse certain things. For example, people sometimes get confused about the distinction between the abbreviations COM, DCOM, MTS, and COM+. In reality, the term COM+ refers to two things. First, COM+ represents the integration of the COM model with the MTS services model. Second, COM+ refers to a series of services that Microsoft provides for you, like distributed transactioning, role-based security, easy deployment of your application, and so forth. The acronym COM in many ways sounds old in comparison to COM+, but this is just a side effect of the marketing effort. In reality, COM and COM+ are the same thing when it comes to how the components are made. COM+ components are COM components, and COM components are now called COM+ components.

With that in mind, the book is organized as follows:

Chapter 1

Explains the progression from COM to DCOM to MTS, COM+, and finally .NET. It is meant to provide you with an overview of what Microsoft has been trying to accomplish with component technology for the last eight years and where we are headed later this year and next year.

Chapter 2

Explains the benefits of using interfaces in your programming and shows how interfaces are crucial for versioning. It also explains why COM uses interfaces.

Chapter 3

Explains what interfaces look like at the memory level. The chapter is meant to expose you to how the VB compiler generates VB COM objects in memory. It also exposes you to the most widely used interfaces in COM, IUnknown and IDispatch.

Chapter 4

Discusses how ActiveX DLLs work. It discusses the difference between the CreateObject function and the New keyword. It also explains how objects are instantiated and examines the process of activation from the client to the server.

Chapter 5

Explains how ActiveX EXEs work. It explains multithreading, including COM’s apartment model. It also explains how COM makes it easy for a client to talk to a remote component, but at the cost of performance.

Chapter 6

Explains how to go about creating new versions of your components that are compatible with old versions. This chapter explains the difference between binary compatibility, project compatibility, and no compatibility. Also, this chapter shows how to write interfaces in IDL.

Chapter 7

Explains what COM+ services are. It also explains how to create a COM+ application and add your components to it. This chapter shows how to deploy COM+ applications to client machines.

Chapter 8

Shows how to write code that interacts with the COM+ services. This chapter also talks about the COM+ architecture and discusses various ways to debug your application.

Chapter 9

First discusses transactions and record locking in general while focusing on SQL Server and Oracle. It then examines how to talk to the Distributed Transaction Coordinator (DTC), which enables you to have multiple database systems involved in the same transaction. At the end of the chapter, you learn the effects of turning on transactioning services for your components.

Chapter 10

Discusses how COM and COM+ security affects the communication between clients and servers. The chapter explains how COM+ security has its roots in RPC security and shows you how to make calls to the server—including requests over the Web—secure.

Chapter 11

Covers the architecture of .NET and how compilers produce Intermediate Language (IL). This chapter also shows the new versioning scheme in .NET, as well as many of the other new features in VB.NET. Thereafter, the chapter shows how to mix both COM+ and .NET.