Object Linking and Embedding

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Object Linking and Embedding (OLE) is a distributed object system and protocol developed by Microsoft.

OLE allows an editor to "farm out" part of a document to another editor and then reimport it. 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 using OLE, next to reduced file size, is the ability to create a master file. References to data in this file can be made and the master file can then have changed data which will then take effect in the referenced document.

Its primary use was for managing compound documents, but it was also used for transferring data between different applications using drag and drop and clipboard operations.

Technology

OLE 1.0, released in 1990, was the evolution of the original dynamic data exchange, or DDE, concepts 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 windows 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, it is stored in native Windows formats (such as a bitmap or metafile), as well as being stored in its own, native format. This native format allows an OLE-aware application to embed a portion of another document cut or copied to the clipboard by the user by storing it in the current document.

OLE 2.0

OLE 2.0 was the next evolution of OLE 1.0, sharing many of the same goals, but was re-implemented over top of the Component Object Model instead of using VTBLs. In 1996, Microsoft renamed the OLE 2.0 technology to ActiveX.

See also

• OLE Automation
• OLE for process control
• Component Object Model (COM)
• Distributed Component Object Model (DCOM)
• Dynamic Data Exchange (DDE)
• Microsoft .NET

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