The fundamental design goal is that OPC HDA Auto interface is intended to work as a 'wrapper' for existing OPC Historical Data Access Custom Interface Servers providing an automation friendly mechanism to the functionality provided by the custom interface. The automation interface provides nearly all of the functionality of the required and optional Interfaces in the OPC Historical Data Access Custom Interface. If the OPC Historical Data Access Custom server supports the interface, the functions and properties at the automation level will work. Automation interfaces generally do not support optional capabilities in the same way that the custom interface does. If the underlying custom interface omits some optional functionality then the corresponding automation functions and properties will exhibit some reasonable default behavior.
Graybox OPC HDA Auto Wrapper is the DLL-module, in which all of the needed OLE-objects are implemented. After registering this module, you will be able to use any OPC HDA Server with almost any OLE enabled programming language (Visual Basic, VBA, etc).