If you want to use some other form of backend, you can use this variable to choose which back end class to use for your general tag storage.
The default is to save databases in flat files. Alternatively, you could write a new database backend that stores tags into a database, or other storage system.
The default type of database created for new files. This can be changed on a per file basis, so that some directories are saved using one mechanism, and some directories via a different mechanism.