The IUnknown interface is a common interface supported by all OLE objects and, therefore, by all speech recognition and text-to-speech objects. This interface allows an application to obtain the addresses of the other interfaces supported by an object and manage the interface pointers that are obtained.
All interfaces contain the IUnknown member functions QueryInterface, AddRef, and Release. This means that once you have the address of any interface for a particular object, it is not necessary to call the IUnknown::QueryInterface member function to obtain the address of another of the object's interfaces.
For more information about the IUnknown interface and its member functions, see the Win32 SDK.