You can make functions, objects, or entities coded in ObjectARX available to developers who access an ActiveX object model through VBA or another programming environment.
In COM applications, you define abstract interfaces that describe the data and functionality of your application. Then you define COM classes, or coclasses, that implement those interfaces. The coclasses can wrap any functionality you desire. For our purposes, the coclass implementations always call ObjectARX-based classes and functions.
Using Microsoft Active Template Library (ATL) makes project setup easier. ATL creates the interface and coclass skeleton for you, based on information that you provide. ATL also gives you complete support for standard ActiveX Automation. ObjectARX extends ATL with its own set of templates that simplify the integration of ObjectARX applications within COM and ATL frameworks.