Layer 1, 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. The composite layered architecture of an SOA can leverage existing systems, integrate them using service-oriented integration.
Layer 2, the component layer, used container based technologies and designs 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 can be used for design of application flow.
Layer 5 Web services at the application interface or presentation level. It is also important to note that SOA decouples the user interface from the components.
Level 6 enables the integration of services through the introduction of reliable and intelligent routing, protocol mediation, and other transformation mechanisms, often described as the enterprise service bus.
Level 7 ensures quality of service through sense-and respond mechanisms and tools that monitor the health of SOA applications, including the all-important standards implementations of Web Services-Management.