WinFS is an idea to use a SQL Database to handle managing documents and files instead of the current way of doing this with Windows XP.
This is being developed for a future release of Windows. Using a database does not have the flexibility of a block storage file system and a programatically handled.
At present databases are used for fixed format data. SQL usually runs on top of a flat file manager. This idea may have some advantages but CardFile was not included with new versions of Windows.