In one of my previous columns on Service Orientation (SO), I introduced the concept of "contract-first" service development. Over the next two installments of this column, I'm going to cover the topic in depth. In this first part, I'll build the case for contract-first development and discuss the ASMX programming model. As a follow-up, I'll walk you through a practical contract-first development process using today's tools and illustrate a hybrid technique that can give you a good balance between interoperability and productivity.
The shift from object-orientation to component development made it possible to build more loosely coupled and flexible systems, in which individual components could evolve independently without affecting the rest of the system. Component technology made this possible by enforcing strict boundaries and restricting access to objects through explicit interface definitions. An interface-based development approach focuses on sharing explicit interface definitions, or "contracts," expressed in a language easily understood by others, removing dependencies on implementation details and offering programming language interoperability. There are valuable design lessons to be learned from the experience with components as SO evolves. One of the most important of these lessons revolves around contract design.
