Dynamic data exchange always takes place between a client application and a server application. The client initiates the exchange by establishing a conversation with the server so that it can send transactions to the server. (A transaction is a request for data or services.) The server responds to these transactions by providing data or services to the client. A server can have many clients at the same time, and a client can request data from multiple servers. Also, an application can be both a client and a server. A client terminates a conversation when it no longer needs a server's data or services.
For example, a graphics application might contain a bar graph that represents a corporation's quarterly profits, and the data for the bar graph might be contained in a spreadsheet application. To obtain the latest profit figures, the graphics application (the client) establishes a conversation with the spreadsheet application (the server). The graphics application then sends a transaction to the spreadsheet application, requesting the latest profit figures.