Client, Server, and Conversation

Two applications participating in dynamic data exchange are said to be engaged in a DDE conversation. The application that initiates the conversation is the DDE client application; the application that responds to the client is the DDE server application. An application can engage in several conversations at the same time, acting as the client in some and as the server in others.

A DDE conversation takes place between two windows, one for each of the participating applications. A window may be the main window of the application; a window associated with a specific document, as in a multiple document interface (MDI) application; or a hidden (invisible) window whose only purpose is to process DDE messages.

Since a DDE conversation is identified by the pair of handles to the windows engaged in the conversation, no window should be engaged in more than one conversation with another window. Either the client application or the server application must provide a different window for each of its conversations with a particular server or client application.

An application can ensure a pair of client and server windows is never involved in more than one conversation by creating a hidden window for each conversation. The sole purpose of this window is to process DDE messages.