NTFS has a database, the MFT. It can index attributes, such as file names, which are a b+tree. A file's $DATA is also placed into the MFT, unless it doesn't fit, then NTFS allocates virtual cluster numbers (more MFT attributes) which point to the on-disk data structure of the file.

All files are represented in a table with rows and columns. "Directories" simply have a special "directory = true" attribute in a row (simplified).

The hierarchy is for you, the human.

Like many file systems, NTFS also contains a log for recoverability/rollback purposes.

It's not quite relational but it doesn't make sense to be relational. Why would you need more than one 'table' to contain everything you need to know about a file? Microsoft experimented with WinFS, which wasn't a traditional file system (it was an MSSQL database with BLOB storage which sat ontop of a regular NTFS volume). Performance was bad and Skydrive replaced the need for it (in the view of MSFT).