What is COM?

Question

I searched hard, but was unable to grasp the whole idea. Can anyone tell me:

• What COM actually is?
• How do GUIDs work, and how are they used by COM? <

Answer 1

COM enables reusable software. Like building blocks, you can create COM objects (or now Assemblies in .NET) to provide functionality to a larger piece of software. I have used COM to provide DB integration for Excel and MS BizTalk. Software like MS BizTalk use COM/Assemblies to extend the processing capabilities of a standard process; you can insert a COM into the message workflow to do more processing than is implemented by Microsoft. COM also allows use of Component Services providing built in object pooling, security, and control interface.

Wikipedia has a good definition of GUID. Note that Microsoft has a formatting that is not necessarly used in the rest of development community.

COM by itself does not resolve DLL version issues. It enables you to extend software incrementally if you use the COM versioning capability. So if you have an application that uses a COM to convert XML to Text (for example) and you want to enhance, you can create a new version (2.0) which you can roll-out slowly as you update the source application to use the new COM. This way you could (if need be) have a switch statement that can still use the old COM if required by system limitations, or use the new one (they would be different DLLs).