Every company starts with a single website or web application, but as a company's online presence grows, many different applications and sites are deployed. With a traditional approach of treating each of these applications as separate solutions, a number of problems occur [...] Service APIs can help you reuse a set of common functionality, which is implemented only once into the service layer. They can also help integrate third party applications in a consistent and robust way, and work around possible performance limitations.
The whitepaper covers the differences between the traditional development model and how the service model changes how you think about your backend. He covers implementation, development, documentation, testing methods and general maintenance down the line.