This is a very slick presentation by Herbert Van de Sompel on OAI-ORE which he's due to give today for a workshop at the INFORUM 2009 15th Conference on Prrofessional Information Resources in Prague. It's on the long side at 167 slides but even if you just flip though or sample it selectively you'll be bound to come away with something.

Describing aggregations of resources is a subject that really has to be of interest to CrossRef publishers.