Object Linking and Embedding

Object Linking & Embedding (OLE) is a proprietary technology developed by Microsoft that allows embedding and linking to documents and other objects. For developers, it brought OLE Control Extension (OCX), a way to develop and use custom user interface elements. On a technical level, an OLE object is any object that implements the IOleObject interface, possibly along with a wide range of other interfaces, depending on the object's needs. Object Linking & Embedding (OLE) is a proprietary technology developed by Microsoft that allows embedding and linking to documents and other objects. For developers, it brought OLE Control Extension (OCX), a way to develop and use custom user interface elements. On a technical level, an OLE object is any object that implements the IOleObject interface, possibly along with a wide range of other interfaces, depending on the object's needs. OLE allows an editing application to export part of a document to another editing application and then import it with additional content. For example, a desktop publishing system might send some text to a word processor or a picture to a bitmap editor using OLE. The main benefit of OLE is to add different kinds of data to a document from different applications, like a text editor and an image editor. This creates a Compound File Binary Format document and a master file to which the document makes reference. Changes to data in the master file immediately affect the document that references it. This is called 'linking' (instead of 'embedding'). OLE is also used for transferring data between different applications using drag and drop and clipboard operations. OLE 1.0, released in 1990, was an evolution of the original Dynamic Data Exchange (DDE) concept that Microsoft developed for earlier versions of Windows. While DDE was limited to transferring limited amounts of data between two running applications, OLE was capable of maintaining active links between two documents or even embedding one type of document within another. OLE servers and clients communicate with system libraries using virtual function tables, or VTBLs. The VTBL consists of a structure of function pointers that the system library can use to communicate with the server or client. The server and client libraries, OLESVR.DLL and OLECLI.DLL, were originally designed to communicate between themselves using the WM_DDE_EXECUTE message. OLE 1.0 later evolved to become an architecture for software components known as the Component Object Model (COM), and later DCOM. When an OLE object is placed on the clipboard or embedded in a document, both a visual representation in native Windows formats (such as a bitmap or metafile) is stored, as well as the underlying data in its own format. This allows applications to display the object without loading the application used to create the object, while also allowing the object to be edited, if the appropriate application is installed. The Object Packager, a component of OLE, shipping from Windows 3.1 up to Windows XP allows a non-OLE object to be 'packaged' so it can be embedded into an OLE client. OLE 2.0 was the next evolution of OLE, sharing many of the same goals as version 1.0, but was re-implemented on top of the COM instead of using VTBLs directly. New features were OLE automation, drag-and-drop, in-place activation and structured storage. Monikers evolved from OLE 1 object names, and provided a hierarchical object and resource naming system similar to URLs or URIs, which were independently invented. Windows now has merged the two technologies supporting a URL Moniker type, and a Moniker URL scheme.