Programming WCF Services, 2nd Edition

Contracts

In WCF, all services expose contracts. The contract is a platform-neutral and standard way of describing what the service does. WCF defines four types of contracts:

Service contracts

Describe which operations the client can perform on the service. Service contracts are the subject of the next chapter, but they are used extensively in every chapter in this book.

Data contracts

Define which data types are passed to and from the service. WCF defines implicit contracts for built-in types such as int and string, but you can easily define explicit opt-in data contracts for custom types. Chapter 3 is dedicated to defining and using data contracts, and subsequent chapters make use of data contracts as required.

Fault contracts

Define which errors are raised by the service, and how the service handles and propagates errors to its clients. Chapter 6 is dedicated to defining and using fault contracts.

Message contracts

Allow the service to interact directly with messages. Message contracts can be typed or untyped and are useful in interoperability cases when another party has already dictated some explicit (typically proprietary) message format. That, however, is by no means the usual case for common WCF applications, so this book makes no use of message contracts. Unless you are required to leverage the flexibility, power, and extensibility of message contracts, you should avoid them, as they add no value but do add complexity. In many cases, the desire to use message contracts ...