The Planets (Preservation and Long-term Access through Networked Services) project has released White Paper: Representation Information Registries.
Here's the "Executive Summary":
This document is a report on the state-of-the-art in the field of Representation Information Registries (RIRs). RIRs are widely recognised as a critical component of digital preservation architecture in general, and a number of such registries are being developed as part of the Planets architecture in particular. This document discusses the development of the concept of representation information, and of the use of registries as a means of exposing that information for use by digital preservation services; it describes the RIR implementations which currently exist or are under development globally; it assesses planned and potential future developments in this area; it discusses the role which RIRs play within the Planets project, and concludes with recommendations for future areas of research within Planets and beyond.