DDE identifies the units of data passed between the client and server with a three-level hierarchy of application, topic, and item names.
Each DDE conversation is uniquely defined by the application name and topic. At the beginning of a DDE conversation, the client and server determine the application name and topic. The application name is usually the name of the server application. For example, in a conversation in which Microsoft Excel acts as the server, the conversation application name is Excel.
The DDE topic is a general classification of data within which multiple data items may be “discussed” (exchanged) during the conversation. For applications that operate on file-based documents, the topic is usually a filename. For other applications, the topic is an application-specific name.
Because the client and server window handles together identify a DDE conversation, the application name and topic that define a conversation cannot be changed during the course of the conversation.
A DDE data item is information related to the conversation topic that is exchanged between the applications. Values for the data item can be passed from the server to the client, or from the client to the server. Data can be passed with any of the standard clipboard formats or with a registered clipboard format. For more information about standard clipboard formats, see the description of the SetClipboardData function in Microsoft Windows Programmer's Reference, Volume 2. For more information about registering clipboard formats, see the description of the RegisterClipboardFormat function. A special, registered format named Link is used to identify an item in a DDE conversation.