Dynamic Data Exchange (DDE)

In a Windows environment, applications can communicate using Dynamic Data Exchange. The application that starts the conversation is called the client. The application which responds is called the server. In DDE, the client determines the topic of the conversation and the items that are exchanged, either by sending them to the server or by requesting them from it. The client may also initiate an advise loop in which it asks to be notified each time a particular item changes. USoft Developer is a DDE server and may act as a DDE client.

Windows applications may initiate conversations with a USoft DDE server about two topics:

·	Field in a currently open window.

·	A SQL script command.

Field topic

The value in this field may be retrieved and changed. The client can also ask to be notified whenever the field value changes.

SQL topic

The client sends such a command to the USoft Developer server, which passes it to the SQL script interpreter. In this way, the client can send data manipulation requests to the server, which are validated by the conceptual processor before they are executed.

USoft Developer supports a number of actions to let you use it as a DDE client. Using these actions, you may initiate a conversation with a DDE server, exchange items, and close the conversation again. These actions are listed in the following table.

Available DDE Actions

Action	Purpose
DdeConnect()	Opens a conversation with a DDE server.
DdeDisconnect()	Closes a conversation.
DdeRequest()	Requests an item from the DDE server.
DdePoke()	Sends an item to the DDE server.
DdeExecute()	Makes the DDE server execute a command.
DdeStartAdvise()	Starts an advise loop, asking the DDE server to notify it whenever a particular item changes.
DdeStopAdvise()	Stops a running advise loop.