This illustration shows two spaces, the Oracle Process Space and the External Process Space.
The Oracle Process Space includes the Oracle Database and possibly user-written PL/SQL scripts (i.e. stored procedures, functions or triggers).
The External Process Space contains the COM feature in which reside the external procedures. The External Process Space also contains the Oracle Listener and External Procedure Handler.
A PL/SQL script would, in the Oracle Process Space, access the database, and in the External Process Space start the Oracle Listener, which would activate the External Procedure handler.
Once the External Procedure handler is activated, it would in turn activate the COM feature.
The COM feature would communicate by COM or DCOM with a COM Automation server and return a result to COM feature which would pass the result to External Procedure handler, which would then communicate back to the database.