What is Known Types in WCF

The Known Attributes enables you to design acceptable derived classes for a given Data Contract.It can be used in the following example.

Example:

[Datacontract()]

[KnownType(typeof(LoanApprovalTask))]

Class task

{

......

}

[Datacontract()]

Class LoanApprovalTask : Task

{

.....

}

When working with polymorphic types in your Service Contract, the KnownTypeAttribute is required because polymorphism is outside the paradigm of Service orientation. For example  you have following Service Contract.

[ServiceContract()]

 Interface ITaskManager

{

   [OperationContract()]

   List<Task> GetTaskByAssignmentName(String name)

}

if some of the objects  being returned by the GetTasksByAssignedName operation are LoanApprovalTask objects, the client can know how to deserialize these more specific tasks only if the KnowntypeAttributes was used.