XTags is a proof-of-concept implementation of a filesystem with nothing but metadata. Files does not exist in directories at all, but "directories" is used to browse files matching metadata.
For my own purposes, it is useful to store anything from mediafiles to documents. For this purpose XTags allows to query for metadata from sources like imdb, anidb, etc, and supports storing a thumbnail.
This implementation is using symlinks and must be manually updated after editing metadata, and only works on directories (on the real filesystem)
# ls tag-test
year:2009 year:2010 year:2011 content-type:image-png content-type:video-x-matroska
# ls tag-test/content-type:image-png
year:2009 year:2010 year:2011 holiday-pictures-2009 holiday-pictures-2010 holiday-pictures-2011 sample-pictures
# ls tag-test/content-type:image-png/year:2010
holiday-pictures-2010 sample-pictures
# ls tag-test/content-type:image-png/year:2010/sample-pictures
sample01.png sample02.png sample03.png sample04.png sample05.png
For each "directory" an intersection is performed, e.g.
content-type:image-png/year:2010 is the intersection of all files tagged with
content-type:image/png and year:2010. It also means that reversing the tags
yields the same result: `year:2010/content-type:image-png".
Custom queries can be made using the xtags cli tool,
e.g. xtags query year:1995-2005.