Ellen Francine Barbosa José Carlos Maldonado Ivan Luiz Marques Ricarte Exploring Learning Objects under Conceptual, Instructional and Didactic Perspectives. 2003 conf/pgldb/2003 PGLDB http://sunsite.informatik.rwth-aachen.de/Publications/CEUR-WS/Vol-70/paper4.pdf db/conf/pgldb/pgldb2003.html#BarbosaMR03