COM (Component Object Model)

(Component Object Model) A component software architecture from Microsoft, which defines a structure for building program routines (objects) that can be called up and executed in a Windows environment. This capability was built into Windows 95/98 and Windows NT 4.0. Parts of Windows itself and Microsoft’s own applications are also built as COM objects. COM provides the interfaces between objects, and Distributed COM (DCOM) allows them to run remotely. COM is used in the following ways.

COM Objects
COM objects can be small or large. They can be written in several programming languages, and they can perform any kind of processing. A program can call the object whenever it needs its services. Objects can be run remotely (DCOM) over the network in a distributed objects environment.

Automation (OLE automation)
Standard applications, such as word processors and spreadsheets, can be written to expose their internal functions as COM objects, allowing them to be “automated” instead of manually selected from a menu. For example, a script could be written to extract data from a database, summarize and chart it in a spreadsheet and place the results into a text document. See COM automation for more info.

Controls (OLE controls, ActiveX controls)
Applications can invoke COM objects, called “controls,” that blend in and become just another part of the program. An industry of third-party, ready-made controls for the Windows programmer has been created. ActiveX controls can also be downloaded from the Internet to make a Web page perform any kind of processing. See ActiveX control for more info.

Compound Documents and ActiveX Documents
Microsoft’s OLE compound documents are based on COM, which lets one document be embedded within or linked to another (see OLE for more info). ActiveX Documents are extensions to OLE that allow a Web browser, for example, to view not only Web pages, but any kind of document.

Programming Interfaces
Increasingly, Microsoft is making its standard programming interfaces conform to the COM object model so that there is continuity between all interfaces. See DAOADO and OLE DB good reading.

Microsoft first used the term OLE to refer to its COM-based architecture, then later dropped that designation in favor of ActiveX. Since both OLE and ActiveX are based on COM, the term COM is also used. As a result, any combination of the words COM, OLE and ActiveX followed by the words control, object and component may mean the same thing, or they may not, depending on context.

2 thoughts on “COM (Component Object Model)

  1. Pingback: .NET Framework – In Short | iiteeeestudents

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