Distributed Objects & Components: COM / COM+ / DCOM / ActiveX / OLE
Intro
"Distributed COM, or DCOM, is an extension of the Component Object Model (COM),
which has been part of the Windows family of operating systems for many years as the underlying framework that makes OLE,
and more recently ActiveX, possible. COM is an object-based framework for developing and deploying software components.
COM lets developers capture abstractions as component interfaces and then provide binary classes that implement those interfaces.
Encapsulation is enforced by COM such that client applications can only invoke functions that are defined on an object's interface.
COM's binary interoperability standard facilitates independent development of software components and supports deployment
of those components in binary form. The result is that ISVs can develop and package reusable building blocks without shipping source code.
Corporate application developers can use COM to create new solutions that combine in-house business objects, off-the-shelf objects,
and their own custom components.
DCOM extends COM to the network with remote method calls, security, scalability, and location transparency.
As DCOM becomes available on platforms other than Windows NT and Windows 95, companies can build software architectures that take advantage
of their existing infrastructure and deploy business objects that access legacy applications and databases." (DBMS and Internet Systems)
"Microsoft Transaction Server (MTS) combines the features of a TP monitor and an object request broker into an easy-to-use package.
Developers use MTS to deploy scalable server applications built from ActiveX components,
focusing on solving business problems instead of on the programming application infrastructure.
MTS delivers the "plumbing" - including transactions, scalability services, connection management, and point-and-click administration -
providing developers with the easiest way to build and deploy scalable server applications for business and the Internet." (Microsoft)
"What, exactly, is COM+? COM+ is many things, but the basic answer is quite simple.
COM+ is the merging of the COM and MTS programming models with the addition of several new features.
COM was created long ago as a workstation-level component technology;
with the release of Distributed COM (DCOM) in Windows NT 4.0,
the technology was expanded to support distributed applications via remote component instantiation and method invocations.
MTS followed. It was designed to provide server-side component services and to fix some of DCOM's deficiencies,
e.g., how it handles security issues, and the complete lack of a component management and configuration environment.
COM+ now comes along to unify COM, DCOM, and MTS into a coherent, enterprise-worthy component technology." (Visual C++ Developers Journal)
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