An application service represents an explicitly defined exposed application behavior.
An application service exposes the functionality of components to their environment. This functionality is accessed through one or more application interfaces. An application service is realized by one or more application functions that are performed by the component. It may require, use, and produce data objects.
An application service should be meaningful from the point of view of the environment; it should provide a unit of behavior that is, in itself, useful to its users. It has a purpose, which states this utility to the environment. This means, for example, that if this environment includes business processes, application services should have business relevance.