DCOM Overview

The OPC device communications enabler for CIMPLICITY is based on Microsoft's Object Linking & Embedding (OLE) model. OLE, in turn, was based on a specification for application architecture called the Component Object Model (COM).

COM is a method of writing a software application–a design model. Its most basic principle is that instead of writing an application as one large mass of code, the application should be broken down into independently running parts that each performs a specific function within an application.

In addition, COM specifies exactly how these components will interact with one another to form the whole application. This is known as the component's interface. The interface is actually a set of functions within the component, which other components can call from outside the component. These functions are exposed to the outside world. Any other component can call these functions to tell the component to do something, or ask it for some result. When a component exposes functions that anyone can call, it is called an OLE Server. Any other component calling an interface function is that server's OLE Client.

Each component is actually a program, running on the computer that may have exposed interfaces. The component program might do a variety of functions including things like displaying a chart, data collection from a PLC via a serial port, etc. Another program could then access the data through the exposed set of interface functions. This is the basic relationship between an OPC Server, and the CIMPLICITY OPC Client communications enabler.

Distributed COM is exactly the same principle as COM, with one important difference. The OLE Server component, instead of just serving up functions to other components running on the same computer, can serve up functions to other components running on ANY computer on the network. Using DCOM, the CIMPLICITY OPC Client can talk to OPC Servers running anywhere on the network.

There are some basic requirements and some configuration necessary to make this happen successfully.

More information

Requirements for Distributed COM.

About the CIMPLICITY OPC Server.

About OPC Client.