Creating applications in a service-oriented style is becoming the norm. For this to happen, the platforms on which those applications are built must provide the right support for creating service-oriented software. Achieving this is one of WCF’s most important goals.
Thinking of an application as providing and consuming services is hardly a new idea. What is new is a clear focus on services as distinct from objects. Toward this end, WCF’s creators kept four tenets in mind during the design of this technology:
n Share schema, not class. Unlike older distributed object technologies, services interact with their clients only through a well-defined XML interface. Behaviors such as passing complete classes, methods and all, across service boundaries aren’t allowed.
n Services are autonomous. A service and its clients agree on the interface between them, but are otherwise independent. They may be written in different languages, use different runtime environments, such as the CLR and the Java Virtual Machine, execute on different operating systems, and differ in other ways.
n Boundaries are explicit. A goal of distributed object technologies such as Distributed COM (DCOM) was to make remote objects look as much as possible like local objects. While this approach simplified development in some ways by providing a common programming model, it also hid the inescapable differences between local objects and remote objects. Services avoid this problem by making interactions between services and their clients more explicit. Hiding distribution is not a goal.
n Use policy-based compatibility. When possible, determining which options to use between systems should rely on mechanisms defined in languages such as WSDL and WS-Policy. The ability for a client to consume a service is based on the intersection of what the client supports and what the service supports.
Service-oriented applications are the successor to the multi-tier applications of the last decade. As the architectural style continues to spread, this approach is becoming the default for a large share of new software. WCF is the foundation for service-oriented applications built on the .NET Framework, which makes it a mainstream technology for Windows-based software.