Svetla Boytcheva Albena Strupchanska Galia Angelova Processing Negation in NL Interfaces to Knowledge Bases. 137-150 2002 conf/iccs/2002 ICCS http://link.springer.de/link/service/series/0558/bibs/2393/23930137.htm db/conf/iccs/iccs2002.html#BoytchevaSA02