Group - OLE Automation

In Microsoft Windows applications programming, OLE Automation (later renamed by Microsoft to just Automation, although the old term remained in widespread use), is an inter-process communication mechanism based on Component Object Model (COM) that was intended for use by scripting languages – originally Visual Basic – but now are used by languages run on Windows. It provides an infrastructure whereby applications called automation controllers can access and manipulate (i.e. set properties of or call methods on) shared automation objects that are exported by other applications. It supersedes Dynamic Data Exchange (DDE), an older mechanism for applications to control one another. As with DDE, in OLE Automation the automation controller is the "client" and the application exporting the automation objects is the "server". Automation was designed with the ease of scripting in mind, so controllers often provide languages such as Visual Basic for Applications to end users, allowing them to control automation objects via scripts. Automation objects can be written in conventional languages such as C++, but the C++ syntax for COM (and therefore Automation) is complex and not very programmer-friendly. In contrast, languages such as Visual Basic and Borland Delphi provide a convenient syntax for Automation which hides the complexity of the underlying implementation. An Automation object is a COM object implementing the IDispatch interface (for details on interfaces and calling conventions, see Component Object Model). Automation objects are referred to as ActiveX objects, while an application that manipulates an ActiveX object is referred to as an ActiveX Client. This interface exposes four methods, the most important of which is Invoke. This method allows calling methods of a class by name, with an arbitrary number of parameters. Neither the name of the method nor the number (and exact types) of parameters need to be known at compile time, as it is the case for COM objects not supporting Automation; moreover, in scripting languages there is no "compile time" at all. This technique is called late binding.