I wrote to the list a few months back asking about expressing FRBR relationships
in MODS. Based on feedback from several people, we have developed a preliminary
implementation of a hierarchical catalog for our collections, which you can try
out here:

One particularly nice example is this page:

The interface is designed to highlight the work/expression/manifestation levels.
Works are defined in MADS records, expressions and manifestations in MODS
records. The system runs in the eXist XML database.

The catalog contains a combination of three collections: Perseus Greco-Roman
materials, a new collection of Civil War-era texts, and several early modern
scientific works, the online versions of which are actually hosted at the Linda
Hall library at U Missouri, Kansas City.

Neither the records nor the interface are entirely consistent yet, or entirely
complient with standards. In particular, the ancient texts do not yet have
classifications and subjects at the work level, and the American collection
doesn't show up in the "genre" column.

David Mimno
Perseus Project, Tufts University