IVOA Recommendation: IVOA Photometry Data Model
  The Photometry Data Model (PhotDM) standard describes photometry filters, photometric systems, magnitude systems, zero points and its interrelation with the other IVOA data models through a simple data model. Particular attention is given necessarily to optical photometry where specifications of magnitude systems and photometric zero points are required to convert photometric measurements into physical flux density units. 
Jesus Salgado, Carlos Rodrigo, Pedro Osuna, Mark Allen, Mireille   Louys, Jonathan McDowell, Deborah Baines, Jesus Maiz Apel...
astro-ph.IM