2.2 Five layer SOA architecture

In our view, the SOA architecture can be viewed as a set of five layers as shown in Figure 1.
This figure shows a model of the ICT environment viewed from the SOA perspective used in the EAI department. The explanation of the five layers as used in the EAI environment in this organisation is as follows:

Figure 1 The five layer SOA model

• Front End
  The Front End (FE) layer represents the front end systems of the ICT environment. Each front end system in this scope can access one or more services in the EAI through a front end adapter.
• Front End Adapter
  The Front End Adapter (FEA) layer represents the services within the EAI scope which offer their services to the front end systems. A FEA service always invokes another service, either on the Composite layer or directly towards a Back End Adapter service.
• Composite
  The Composite layer represents the services within the EAI scope which combine the functionality of other services. A Composite service always invokes another service, either again on the Composite layer or directly towards a Back End Adapter service.
• Back End Adapter
  The Back End Adapter layer represents the services within the EAI scope which represent the services offered by the back end systems. A FEA service always invokes another service, either on the Composite layer or directly towards a Back End Adapter service.
• Back End
  The Back End layer represents the back end systems of the ICT environment. Each back end system in this scope can be accessed by one or more services in the EAI through a back end adapter.