WCF Contracts and Backward Compatibility

Adding new parameters to an operation signature

Client unaffected. New parameters initialized to default values at the service.

Removing parameters from an operation signature

Client unaffected. Superfluous parameters pass by clients are ignored, data lost at the service.

Modifying parameter types

An exception will occur if the incoming type from the client cannot be converted to the parameter data type.

Modifying return value types

An exception will occur if the return value from the service cannot be converted to the expected data type in the client version of the operation signature.

Adding new operations

Client unaffected. Will not invoke operations it knows nothing about.

Removing operations

An exception will occur. Messages sent by the client to the service are considered to be using an unknown action header.

Add new non-required members

Client unaffected. Missing values are initialized to defaults.

Add new required members

An exception is thrown for missing values.

Remove non-required members

Data lost at the service. Unable to return the full data set back to the client, for example. No exceptions.

Remove required members

An exception is thrown when client receives responses from the service with missing values.

Modify existing member data types

If types are compatible no exception but may receive unexpected results.