For a document repository, does it make more sense to:

1.) Tie metadata to a given document
2.) Have a central directory for metadata that is independent of the document collection

A decent UI will more or less abstract that issue away from the user, of course, but I'm concerned about design issues. The repo is atomic, and it's not difficult to query, so I see the issues as kinda breaking down like this:

2.) is easier to manage at the collections level (duh), and assets such as binary files can be introduced into the system without having to create metadata documents to accompany them, however a risk of collisions within the metadata index exists, since changes to different documents can trigger changes to the same metadata file.
1.) is arguably less manageable, but no significant risk of collisions. Also, #1 makes it easier to index documents with something like solr -- although updates across the repo & solr and *not* atomic, so there exists a risk of the index getting out of sync with the collection.

There exists a third option: have the metadata dir that shadows the document dir. This more or less eliminates the risk of collisions, but... well, I'm not sure what the point would be, honestly.