Microsoft developed the Component Object Model, or COM, as the mechanism for communicating between applications and components running on the Windows platform .Developers can use COM to create reusable software components, link components together to build applications, and take advantage of Windows services .
Microsoft originally designed COM to enable communications between components and applications running on the same computer .COM was followed by DCOM (distributed COM), which allowed applications to access components running on other computers over a net-work .
DCOM was itself followed by COM+ .COM+ incorporated features such as integration with Microsoft Transaction Server so applications could group operations on components together into transactions. COM+ provided additional capabilities such as automatic resource management and asynchronous operations.
Enterprise Services, .NET Remoting
COM+ was followed in turn by the .NET Framework, which further extended the features available .Microsoft renamed the technology yet again to Enterprise Services .The .NET Framework also provided several new technologies for building networked components .One example was Remoting, with which a client application could access a remote object hosted by a remote server application as though it were running locally, inside the client application .
A Web service is an application or component that executes on the computer hosting the Web site rather than the user’s computer .A Web service can receive requests from applications running on the user’s computer, perform operations on the computer hosting the Web service, and send a response back to the application running on the user’s computer . Web services use SOAP to communicate.
Windows Communication Foundation (WCF)
Windows Communication Foundation (WCF) is a framework for building service-oriented applications. Using WCF, you can send data as asynchronous messages from one service endpoint to another. The messages can be as simple as a single character or word sent as XML, or as complex as a stream of binary data. WCF provides a model with which you can implement services that conform to many commonly-accepted styles and standards.