IT Architectures and Middleware: Strategies for Building Large, Integrated Systems, Second Edition

15. Changing and Integrating Applications

There is plenty of literature about implementation design for new applications. There is very little on the very real problem of implementation design where applications already exist. This chapter is about changing existing applications, in particular, transaction applications. We also take a look at batch programs because they remain significant in many environments.

In Chapter 14, the subject of changing existing applications was addressed in the context of the data tier. In this chapter, the concern is the presentation and processing tiers; this chapter is about programs, not data.

We will start by discussing again the order processing example used in Chapter 1. First let us recall the “before” state, ...