How will ESA change how applications are designed and built?
Perhaps the most important aspect of the ESA stack to keep firmly in mind is that it does not live in just one application. The ESA stack exists in every part of a network of service consumers and in service providers that are participating to automate a process. Figure 1-11 shows the transition to this architecture from the mainframe stack.

Figure 1-11. Application structure in ESA
Service consumers use the ESA stack to do their jobs, as do service providers. Each type of application may use more or less of each layer in the stack.
The layers of the ESA stack are also constructed differently than in the mainframe era, in which development was performed primarily with languages such as Java, ABAP, and C/C++. All of these languages are still used in ESA, but their focus is to build components that fit into a composition environment in which modeling is the primary method of building applications. Chapter 12 covers how composite applications are structured and how model-driven development tools are used to build them.
Figure 1-12 illustrates how development tasks are separated between developers and programmers who focus on the more technically challenging task of creating enterprise services, and business analysts and process experts who use modeling and orchestration techniques to assemble new applications from existing parts. ...