Layer 1 which is the bottom layer describes operational systems. This layer contains existing systems or applications including existing CRM and ERP packaged applications, legacy applications and “older” object-oriented system implementations as well as business intelligence applications. The composite layered architecture of an SOA can leverage existing systems, integrate them using service-oriented integration.
Layer 2 is the component layer which used container–based technologies and designs used in typical component-based development.
Layer 3 provides for the mechanism to take enterprise scale components, business unit specific components and in some cases project specific components and provides services through their interfaces. The interfaces get exported out as service descriptions in this layer, where services exist in isolation or as composite services.
Level 4 is an evolution of service composition into flows or choreographies of services bundled into a flow to act as an application. These applications support specific use-cases and business processes. Here, visual flow composition tools such as WebSphere WBI-Modeler can be used for design of application flow.
Layer 5, the presentation layer is usually out of scope for an SOA. However, it is depicted because some recent standards such as Web Services for remote Portlets version 2.0 may indeed leverage Web Services at the application interface or presentation level. It is also important to note that SOA decouples the user interface from the components.