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Contracts in WCF, provide interoperability they need to communicate with the client.

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Service Contracts

Service contract describes the operations, or methods, that are available on the service endpoint, and exposed to the outside world.

A Service contract describes the client-callable operations (functions) exposed by the service, apart from that it also describes.

 

Data Contracts

Data contracts help to disambiguate data types on the transmission wire and provides a versioning mechanism. This is usually consistent across all data contracts for the application, and is often similar to the service contract namespace using a “schemas” prefix.

 

Message Contracts

Message contracts provide control over a SOAP message for a service operation request or reply. Message contracts supply a type with the MessageContractAttribute as the only parameter to a service operation and as the return type

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Fault Contract

Fault Contract provides documented view for error accorded in the service to client. 

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