(1) User Layer
provides the external interface (GUI, Web-based or batch commands)
and the management of user interactions (the sequence of user activities within a use case).
(2) Workflow and Process Control Layer
manages complex, automated business processes that interact with many business services.
(3) Business Service and Legacy Wrapping Layer
provides the implementation of the business rules and the operational activities.
(4) Data and Operating System Services Layer
provides the functionality that interacts with the persistent storage environment, including database management systems and file systems. These components are often heavily dependent on application programming interfaces provided by the operating system on which they execute.