THE GOAL OF THIS CHAPTER IS TO INTRODUCE SOA AS A CONCEPT. MY AIM IS TO OUTLINE THE fundamental aspects of SOA, and to show you the circumstances in which its use is appropriate. The important point is that SOA is a paradigm (or concept, or philosophy) that leads to a value system for large distributed systems with different owners.
I will cite, compare, and discuss definitions from various existing sources, such as the OASIS SOA Reference Model, Wikipedia.org, and some books. I will show how and why these definitions differ, and point out the key aspects of SOA that emerge.
It is hard to find an exact definition of the term SOA. The problem is not that there aren’t any definitions; the problem is that there are many different definitions. To give you an idea of how they are similar and dissimilar, a selection of published definitions are sidebars in this chapter. You’ll find some common phrases and attributes as you read them, but you will also find a lot of differences in the context, level of abstraction, and wording.
However, at least all definitions agree that SOA is a paradigm for improved flexibility.