Cheun Ngen Chong Ricardo Corin Jeroen Doumen Sandro Etalle Pieter H. Hartel Yee Wei Law Andrew Tokmakoff LicenseScript: a logical language for digital rights management. 284-331 2006 61 Annales des Télécommunications 3-4 db/journals/adt/adt61.html#ChongCDEHLT06