SubjectPredicateObjectGraph
http://historyofwork.iisg.nl/detail_dir.php?know_id=6595
Dept. of Sociology, University Laval, Quebec, Canada
http://www.uqac.uquebec.ca/balsac
Refereed when creating the manual
http://historyofwork.iisg.nl/detail_dir.php?know_id=6598
History Data Archive, University of Essex, UK