Postgres Plus Advanced Server Oracle Compatibility Developer's Guide :
DROP DIRECTORY -- remove a directory alias for a file system directory path
DROP DIRECTORY name
DROP DIRECTORY drops an existing alias for a file system directory path that was created with the CREATE DIRECTORY command. To execute this command you must be a superuser.
When a directory alias is deleted, the corresponding physical file system directory is not affected. The file system directory must be deleted using the appropriate operating system commands.
The name of a directory alias to be removed.
Remove the directory alias named empdir:
DROP DIRECTORY empdir;