Craig,

You are correct. Your class tree starts out looking like:

Form
   frmBase
      frmData

and would end up looking like:

Form
   frmBase
      frmData
         APPData
      APPBase

>I have a base form called frmBase from which I create a new class called frmData, these are both very generic classes which could be used by multiple apps.
>
>If I create a new app, theory suggests I should subclass these again for my new application, let's call it APP. If I extend frmBase to the new application and call it APPBase, then extend frmData to APPData I have a problem because any changes I make to APPBase will not be reflected in APPData.