input: [Category] Data Contracts [Description] When serializing a data contract type into or from a service operation, the compiler will gladly let you pass in a sub class of the data type. However, this will by default fail the call because WCF will not know how to serialize or deserialize the sub class. For that, you have to apply the KnownTypeAttribute at the proxy or contract level, as show in The download. You will also need to apply the attribute on the service side if the service needs to return matching sub classes. [Last Updated] 9/7/2006 [Title] 
output: Class Hierarchy