Provides implementations of the "backed" wrappers for the mutable Second Class Objects (SCO's) that are supported. All have a "backing store" allowing the contents to be sent to/retrieved from the datastore when required. Please refer to section 6.3 of the JDO 1.0 spec. Also provides queueing so that optimistic transactions can be supported when used with the backing store. All "backed" wrappers extend the basic form of the wrapper in the parent package.