In addition to dependencies, applications often use a weak relationship to describe notifications and messages. These are encapsulated by JavaBean events. An event is designed into a source bean when one or more listener Beans wish to be notified of some event that takes place on the source bean. This is described as a weak relationship because neither bean needs to know about the other in order to run. While the application might require the connection in order to work properly, the components themselves do not require it. Logging, for instance, uses JavaBean events: individual components do not require listeners for their log events, but the application as a whole usually requires certain logging connections to be in place. For more information, see Events and Event Listeners in the Core ATG Services chapter.

Nucleus configuration files can establish event source/listener relationships. The event source configuration file specifies which components act as event listeners, and Nucleus automatically makes the connections.

After establishing the architecture, components, dependencies, and configuration of the application, the developer can then hand the whole application over to Nucleus and watch it run.