Contracts

Windows Communication Foundation (WCF, formerly known as Indigo) is built upon the foundation of web services messaging and related standards, while at the same time makes it possible to serialize messages in a more compact binary format, or in a more proprietary way. Still, the core message can always be represented in XML, therefore be considered compatible with any platform that understands XML, and agrees on the contract that defines said messaging between systems.
The contract is a platform-neutral and standard way of describing what the service does. WCF defines four types of contracts:

• Service Contract
• Data Contract
• Message Contract
• Fault Contract