4.3.2 Automation servers and COM objects

An Automation server can implement more than one dispinterface, but it will normally implement a single COM object, to which a controller can connect and which it can query to obtain the dispinterfaces it contains.

The description of the COM object as a whole is called a coclass, which stands for COM class. Each such kind of object is identified by a Class ID. A Class ID is a GUID ("Globally Unique IDentifier"), a 128-bit number. (Also sometimes called a UUID--"Universally Unique IDentifier").

The following is an example of a GUID that could be used as a Class ID:

e90f09e0-43db-11d0-8a04-02070119f639

For more on GUIDs, see Section 2.2.5 on page 123.

When an Automation controller wants to use a particular Automation service, it requests an instance of a COM object with a particular Class ID. The Microsoft OLE/COM libraries then arrange for the controller to either connect to an already running server for objects of that Class ID, or start a new server running. It finds out which server to run by looking up the Class ID in the Windows Registry, where it will find the pathname of the server application to be run.

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OLE, COM, ActiveX and DBMS Reference - 31 MAR 2000