Currently "implementation id" is serialized with simpleframework. Instead it should use the SerializationService (through the simple core OpenmrsSerializer) to convert to/from strings for persistence.
(The reason is that we want to stop using simpleframework generally.)
See the AdministrationService and AdminsitrationServiceImpl for the implementation id methods to convert.
The xml format should stay the same so that users that are upgrading do not have to worry about losing their currently serialized implementationid.