If no backend is provided during initalization or if the context
contains an Offline
flag that is true , then offline mode
is activated. This may fail, if the offline cache has not been filled
during a previous execution.
Less entities may be available from XBackendEntities ,
when operating in offline mode than when operating with an online
SingleBackend .
If offline mode is not invoked, the implementation behaves
like any other BackendAdapter .