Peter F. Patel-Schneider Dieter Fensel Layering the Semantic Web: Problems and Directions. 16-29 2002 conf/semweb/2002 International Semantic Web Conference http://link.springer.de/link/service/series/0558/bibs/2342/23420016.htm db/conf/semweb/semweb2002.html#Patel-SchneiderF02