Given a collection of files which will have associated metadata, what are the recommended methods for storing this metadata?
Some files formats support storing metadata internally (EXIF,ID3,etc), but not all file formats support this, so what are more general options?
Some of the metadata would almost certainly be unique (titles/descriptions/etc), whilst some would be repetitive to varying degrees (categories/tags/etc).
It may also be useful to group the metadata, if different types of attribute are required.
Ideally, solutions should cover concepts, rather than specific language implementations.