Class SimpleMsg
  'member variable to store the message text
  Private strMessage As String

  'property to allow get/set functionality on 
  'strMessage member variable
   Public Property MsgText() As String ...
End Class

Class SmartMsg
  Inherits SimpleMsg

  Private FileName As String

   Public Sub New(ByVal FileName As String) ...

   Public Sub Dispose() ...

   Public Function Write() As Boolean ...
   Public Function Read() As Boolean ...
End Class