Overview

DCOM is much easier to understand if you first see how all the different parts that make up the "middleware" services fit together and what they are. In this chapter I describe each service in brief, showing where it fits in relation to the others. In the following chapters each one of these services is described in detail.

I always believe a picture helps enormously in an explanation. Below you find a diagram I will be using throughout the rest of the book, which shows the parts of DCOM in overview.

DCOM is an architecture that groups a set of services used to build distributed systems. Unfortunately what constitutes a DCOM service and what doesn't isn't that precise within Microsoft's own literature, but we have defined it to mean any service capable of being used to build distributed systems, then we get round the problem of whether MSMQ is DCOM or not, whether MTS is DCOM and so on.

COM Interface

All the services of DCOM are accessible via the COM interface a component- and interface-based interface to all the services of DCOM not only application components. Put another way, DCOM services are invoked in exactly the same way as a developer may invoke the methods on an application component.

Thus, to access security services, for example, the programmer invokes security methods on security classes. Similarly, to use the Transaction services in MTS, the programmer uses classes and methods specifically designed to handle distributed transactions. In effect, the...