WCF SDK Question:

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. There are two types of Service Contracts.
ServiceContract - This attribute is used to define the Interface.
OperationContract - This attribute is used to define the method inside Interface.
[ServiceContract]
interface IMyContract
{
[OperationContract]
string MyMethod( );
}
class MyService : IMyContract
{
public string MyMethod( )
{
return "Hello World";
}
}
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 we can easily define explicit opt-in data contracts for custom types.
There are two types of Data Contracts.
DataContract - attribute used to define the class
DataMember - attribute used to define the properties.
[DataContract]
class Contact
{
[DataMember]
public string FirstName;
[DataMember]
public string LastName;
}
If DataMember attributes are not specified for a properties in the class, that property can't be passed to-from web service.
Fault contracts:
Define which errors are raised by the service, and how the service handles and propagates errors to its clients.