A COM component provides reusable, encapsulated functionality to client programs
running in a Windows environment. You can use VB to create one of the several
types of COM components.
A COM component's threading model affects the way that the COM component handles
requests from clients and manages memory.
An object is externally creatable when an application that can serve as an
ActiveX client can declare an instance of (that is, instantiate) that object as
a variable and then manipulate the methods and properties of that object.
You can register your server component in the Windows Registry in one of several
ways. These ways are discussed in more detail in the section titled "Registering
and Unregistering a COM Component." A Visual Basic project provides an externally
creatable object through certain project settings and by possessing a class module
whose properties you have set appropriately.
An externally creatable object also typically provides a gateway to other objects
that can't be directly created by clients. Every COM component provides at least
one externally creatable object. The server component's externally creatable objects,
together with the other objects indirectly exposed by the externally creatable
objects, is known as an object hierarchy or object model.
You can implement your own COM component's object model with custom object
classes. Although you can create custom object classes specific to a single application,
Microsoft's published documentation and courseware are full of examples of classes
used to implement COM components.