With an understanding of COM and universal data access (UDA), developers can easily create the business and data access logic required by distributed applications. However, as we saw in Chapter 1, a great deal of infrastructure is needed to make distributed applications work in a multiuser environment.
In Microsoft Windows NT 4.0, Microsoft Transaction Server (MTS) provides this infrastructure. With the advent of Windows NT 5.0, COM and MTS will merge to form COM+. Although we'll discuss MTS as a separate product, you should really think of it as an extension of COM—"COM-not-quite-+," if you will. MTS is simply a set of COM services for building component-based application servers, the middle tier of the three-tier application architecture.
By the end of this chapter, you should understand the services offered by MTS and how they relate to the basic COM services discussed in Chapter 2 as well as to traditional transaction processing systems. You should also have a good understanding of the application server programming model.
The ideas presented in this chapter will still apply when COM+ is available. However, some of the details of how things work will change. Chapter 16 provides an overview of COM+ and how it will impact the material covered in this book.