Hasan M. Jamil Gillian Dobbie A Model Theoretic Semantics for Multi-level Secure Deductive Databases. 130-147 2002 conf/iclp/2002 ICLP http://link.springer.de/link/service/series/0558/bibs/2401/24010130.htm db/conf/iclp/iclp2002.html#JamilD02