The sqlfs filesystem implements a POSIX style file system on top of an SQLite
database. It allows applications to have access to a full read/write
file system in a single file, complete with its own file hierarchy and name
space.  This is useful for applications which needs structured storage, such
as embedding documents within documents, or management of configuration
data or preferences.

WWW: http://www.nongnu.org/libsqlfs/