FileDatastore is a concrete class. An FileDatastore object is
used in the program to store/restore the geometry and state information
in the domain at particular instances. This information is stored in
binary form in files. As no standard format is used for the storage of
integers and double values, files used to store the data on one type
of machine, may not be read by a FileDatastore object on another type
of machine where the storage of integers and doubles is different.
int dbTag