One LEGO block by itself is no fun at all.
– Jason Bloomberg
The return on investment (ROI) of SOA is achieved by providing business value and solving real-world problems, and you can solve these problems only if your business processes drive the technology — not the other way around. As discussed in Chapter 4, BPM provides the business process workflow that drives how you define business-level services and how you can compose existing services to form new applications and services. Services are reusable components and are meant to be combined to meet business needs for enterprise applications. Service composition is the practice of how this objective is achieved.
Good service composition is an art form, building on sound architectural principles and successful design patterns. Certain strategies are successful, other strategies are flawed from the beginning, and the success of many strategies depends on specific use cases and a number of different factors. This chapter provides a practical guide for composing services, applying concepts addressed in previous chapters. Earlier in this book, in Chapter 2, we introduced you to SOA fundamentals, and in Chapter 4, we provided an in-depth discussion on Business Process Management (BPM). This chapter builds on those two chapters, and it focuses on the following: