Interface which must be implemented by objects which take part in the
JDBC driver <-> jbase_agent communication.
Note: the interface is not compatible with standard Java
java.io.Serializable. This is because we do not intend to implement Java
serialization protocol for our purposes (note: this is about Java <-> C++ communication).
Each class implementing this interface should have a counterpart
on the server side with compatible serializing/deserializing protocol.