Yes. In this interview Michael Stonebreaker, one of the original developers of PostgreSQL, discusses (among other topics) replacing the file system with a database :
replyThis is one of those perennial ideas; let's get rid of hierarchical file systems and just keep all the files in a database. Speaking as a user who knows how to keep things organized, I like hierarchical file systems. Store the data in a database if you like, but don't break my metaphor.
replyI like a hierarchy, too. Presumably the underlying engine could be a database but it would at least appear to the user as a tree. But with the option to find files with SQL or a SQL-like language. I would love to be able to find files based on all kinds of metadata that was available for searching with the OS’s file system, and not using any special tools. I’m thinking things like EXIF data, audio file metadata, text file line count, and so on.
replyI want to see a kernel managed by NETCONF.
replyNot the XML protocol, that's annoying (although usable) but the structured data model.