Status of an editable persistent object, which can be :
TO_CREATE : The object is in memory but has not been persisted/commited yet
TO_UPDATE (dirty) : The object has been modified in memory but its changed state has not been persisted/commited yet
TO_REMOVE : The object that is in memory has been marked for deletion, which has not occured yet at the persistence layer
NO_CHANGE : The object in memory is sync with its persistent state
These states are useful when you want to remind what to do on a set of Editable objects to get them sync.