Services

Services are the key building blocks in an SOA. You know from the previous chapters that services provide access to well described functionality in an easy-to-use and transparent fashion for service consumers. They are composed of three parts:

• Interface

• Contract

• Implementation

There are three approaches to building services and linking interfaces to the implementation: top-down, bottom-up, and meet in the middle development.

In top-down or contract-first development , the service interface is the starting point for developing services. A framework is used to generate a code skeleton based on the service WSDLs and XSDs. The generated implementation can then be completed. This can be a good approach when there is no service implementation yet in place.

Bottom-up development works the other way around; the interface is generated based on an existing implementation thereby exposing its functionality. Bottom-up development can be a fast way of creating interfaces but gives you less...