L. SWCLOS exploited the principle of monotonicity and a 
number of entailment rules in order to realize the forward referencing for 
objects. See SWCLOS <a 
href="http://iswc2004.semanticweb.org/demos/32/">paper1</a>, <a 
href="http://www.mel.nist.gov/msid/conferences/SWESE/repository/8owl-vs-OOP.pdf">paper2</a>, 
<a href="http://www-kasm.nii.ac.jp/papers/takeda/06/koide06aswc.pdf">paper3 at 
ASWC2006</a>, and <a 
href="http://portal.acm.org/citation.cfm?id=1562868.1562872">paper4 at 
ELW2009</a> on theoret