It allows server applications to make information available to client applications about the type of objects they create.Server applications must register the services they provide in the Windows system registration database. The registration database, located in a file named REG.DAT, has two main purposes:
It allows server applications to make information available to client applications about the type of objects they create.
It allows the OLE libraries to find the server application when the user double-clicks on an object previously embedded or linked in a container document.
As an example, consider an OLE drawing server application. To make itself available to other client applications, it must register itself in the registration database with a unique ClassName that indicates the type of objects it can process (drawings). Whenever an object created by the drawing server application is embedded into or linked to a container document, this unique ClassName is associated with that object. The client application then uses the ClassName to query the registration database to gather specific information about the server draw application.