Learning DCOM

Distributed COM

COM supports interoperability within the confines of a single machine, but DCOM extends COM to support distributed objects. This extension adds support for location transparency, remote activation, connection management, concurrency management, and security. In fact, many presenters and writers speak of DCOM as “COM with a longer wire.” If you come from a traditional distributed objects world and like to keep your terms straight, DCOM is broadly regarded as the “Microsoft ORB.”

As seen in Figure 2-2, the DCOM wire protocol is built on top of Microsoft RPC, Microsoft’s implementation of DCE RPC. This upper layer is termed ORPC, since it is a protocol that supports object-oriented remote procedure calls. You might have guessed that the “O” in ORPC stands for Object.

Figure 2-2. Distributed COM is built on top of DCE RPC

Simply put, DCOM allows developers to concentrate their efforts on developing the functionality of their applications, without the worries of data marshaling and network protocol management. DCOM provides this support for easy distribution of objects in the global cyberspace. Its accessibility is superb, because it is an integrated part of Windows NT, Windows 95, Windows 98, and future Windows platforms.^[3] Soon, it will be supported on a variety of UNIX platforms; check out Software AG’s “EntireX DCOM” product line at http://www.sagus.com.

This book tries ...