Eladio Garví José Samos Manuel Torres Definition of Derived Classes in ODMG Databases. 644-653 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3180&spage=644 2004 conf/dexa/2004 DEXA db/conf/dexa/dexa2004.html#GarviST04