The webMethods Broker system provides you with tools and libraries for building powerful, event-based applications that are made up of de-coupled client programs. The client programs are de-coupled because they communicate by sending and receiving events through a third entity called a Broker. A Broker is actually part of a Broker Server, which may contain multiple Brokers.

The figure below shows a simple example where an Order Entry program receives input from a customer and publishes a CustOrder event. The act of publishing the event causes the event to be sent to the Broker. The Broker then determines that the Order Database program has subscribed to the CustOrder event, and so the Broker distributes the event to the Order Database client program.

More complex applications are possible than the simple example shown in figure below. The Order Database program could create an OrderConfirmed event that would be sent to the Order Entry program as a reply to a CustOrder event.

You might also design a system where several client programs receive the CustOrder event and perform their own processing, such as checking the inventory on hand or verifying the customer's credit status.

The webMethods Broker system also allows the Broker and the client programs that comprise an application to execute on different hosts within a network.