DDE ( Dynamic Data Exchange) and OLE (Object linking and embeding)

Dynamic Data Exchange
Dynamic Data Exchange (DDE) is a technology for communication between multiple applications under Microsoft Windows or OS/2. Overview
Dynamic Data Exchange was first introduced in 1987 with the release of Windows 2.0. It used the "Windows Messaging Layer" functionality within Windows. This is the same system used by the "copy and paste" functionality. Therefore, DDE continues to work even in modern versions of Windows. Newer technology has been developed that has, to some extent, overshadowed DDE (e.g. OLE, COM, and OLE Automation), however, it is still used in several places inside Windows, e.g. for Shell file associations.
The primary function of DDE is to allow Windows applications to share data. For example, a cell in Microsoft Excel could be linked to a value in another application and when the value changed, it would be automatically updated in the Excel spreadsheet. The data communication was established by a simple, three-segment model. Each program was known to DDE by its "application" name. Each application could further organize information by groups known as "topic" and each topic could serve up individual pieces of data as an "item". For example, if a user wanted to pull a value from Microsoft Excel which was contained in a spreadsheet called "Book1.xls" in the cell in the first row and first column, the application would be "Excel", the topic "Book1.xls" and the item "r1c1".
Note: In DDE, the application, topic and item are not case-sensitive.
A common use of DDE was for custom-developed applications to control off-the-shelf software. For example, a custom in-house application might use DDE to open a Microsoft Excel spreadsheet and fill it with data, by opening a DDE conversation with Excel and sending it DDE commands. Today, however, one could also use the Excel object model with OLE Automation (part of COM).
While newer technologies like COM offer features DDE doesn't have, there are also issues with regard to configuration that can make COM more difficult to use than DDE.
[edit] NetDDE
A California-based company called Wonderware developed an extension for DDE called NetDDE that could be used to initiate and maintain the network connections needed for DDE conversations between DDE-aware applications running on different computers in a network and transparently exchange data. A DDE conversation is an interaction between client and server applications. NetDDE could be used along with DDE and the DDE management library (DDEML) in applications.
Object Linking and Embedding
Object Linking and Embedding (OLE) is a technology that allows embedding and linking to documents and other objects, developed by Microsoft. It is found on the Component Object Model. For developers, it brought OLE custom controls (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.
Overview
OLE allows an editor to "farm out" part of a document to another editor and then re-import 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 is to display visualizations of data from other programs that the host program is not normally able to generate itself (e.g. a pie-chart in a text document), as well 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. This is called "linking" (instead of "embedding").
Its primary use is for managing compound documents, but it is also used for transferring data between different applications using drag and drop and clipboard operations. The concept of "embedding" is also central to much use of multimedia in Web pages, which tend to embed video, animation (including Flash animations), and audio files within the hypertext markup language (such as HTML or XHTML) or other structural markup language used (such as XML or SGML) — possibly, but not necessarily, using a different embedding mechanism than OLE.