Leopoldo E. Bertossi, Gyula O. H. Katona, Klaus-Dieter Schewe, Bernhard Thalheim: Semantics in Databases, Second International Workshop, Dagstuhl Castle, Germany, January 7-12, 2001, Revised Papers. Lecture Notes in Computer Science 2582, Springer 2003, ISBN 3-540-00957-4