You're talking about a theoretical implementation of a filesystem with a back-end in a relational database. The question is only whether the information is available.

Say directories map to databases and files map to tables and views. You can create new tables and views by either writing data or an appropriate query. Views and result files would be read-only while data files would be writable. Writing to a data file would be done with a query which modifies the table and the result could be retrieved by then reading the file -- the modification time would be the time of the last update which is known.

Views and queries could be cached results from the last time they were ran which could be updated/rerun by touching them or they could be dynamic and update whenever a table they reference is updated.