.NET - COM(+) 090903

- Referred to ‘MSDN -> Win32 and COM Development’  

 

COM objects can be created with a variety of programming languages. Object-oriented languages, such as C++, provide programming mechanisms that simplify the implementation of COM objects. These objects can be within a single process, in other processes, even on remote computers.

 

To understand COM (and therefore all COM-based technologies), it is crucial to understand that it is not an object-oriented language but a standard. Nor does COM specify how an application should be structured; language, structure, and implementation details are left to the application developer. Rather, COM specifies an object model and programming requirements that enable COM objects (also called COM components, or sometimes simply objects) to interact with other objects. These objects can be within a single process, in other processes, and can even be on remote computers. They can have been written in other languages, and they may be structurally quite dissimilar, which is why COM is referred to as a binary standard; a standard that applies after a program has been translated to binary machine code.

 

Besides specifying the basic binary object standard, COM defines certain basic interfaces that provide functions common to all COM-based technologies, and it provides a small number of functions that all components require. COM also defines how objects work together over a distributed environment and has added security features to help provide system and component integrity.

 

COM is the foundation technology for Microsoft's OLE (compound documents) and ActiveX (Internet-enabled components) technologies.

 

 

COM+ is an evolution [ˌi:vəˈlu:ʃən] of Microsoft Component Object Model (COM) and Microsoft Transaction Server (MTS). COM+ builds on and extends applications written using COM, MTS, and other COM-based technologies.

 

COM+ handles many of the resource management tasks that you previously had to program yourself, such as thread allocation and security. COM+ also makes your applications more scalable by providing thread pooling, object pooling, and just-in-time object activation.

 

COM+ provides several security features that you can use to help protect your COM+ applications, ranging from services to APIs you can call within code.

 

The COM+ object pooling service enables you to configure a component to have instances of it kept active in a pool, ready to be used by any client.

 

Just-in-time (JIT) activation is an automatic COM+ service that can help you use server resources more efficiently, particularly when scaling up your application to do high-volume transactions.

 

但是它的不足是依赖于Microsoft的操作系统平台，因而在其它开发系统平台(如Unix、Linux)上不能发挥作用。