Section 4.20. What is event-driven architecture?

4.20. What is event-driven architecture?

Services are request/response mechanisms. A service consumer makes a request and a service provides a response. Essentially, a service consumer calls the service operation of a service, and the information flows through the service interface. Then the service implementation processes the request and provides the information to the service interface that responds.

However, what happens when there is no requestor, and instead something happens that triggers a chain of activityfor example, a sensor shows that the temperature of a tank in a chemical plant is too high or a business object monitoring the inventory level of a product shows that it has dropped too low? Each of these things is an event. Event-driven architecture (EDA) is the architectural paradigm used to describe systems that are built to react to various events that may occur. In general, once an event is raised somehow, the program that is notified that the event has occurred attempts to respond appropriately. If the tank temperature is too high for a well-known reason, one of several planned responses may be initiated. If the program cannot figure out what to do, an alert may be raised so that some human being can look at the issue and attempt to take corrective action.

Because of the way in which EDAs constantly wait and observe, companies frequently use them to help implement various forms of business activity monitoring. Because they generally attempt to provide an automated response, EDAs are also associated with the management-by-exception paradigms.