dbf_storage provides DBase-formated file-based storage for
datasets. It uses the dbfpy Python package available at
http://sourceforge.net/projects/dbfpy.
The constructor of this class expects an entry storage_location in its
arguments. It should be a base directory on a hard drive where
the data will be stored to and loaded from.
For this storage class, all implemented methods of the storage interface which
accept a table_name parameter interpret it as a file name (relative to the
base directory) without an extension in which the data are stored in an ``.dbf''
file. The extension ``.dbf'' is added automatically. Each table is stored in one
file. The format of these files is described at
http://www.clicketyclick.dk/databases/xbase/format/data_types.html#DATA_TYPES.