Serge Abiteboul Richard Hull Victor Vianu Sheila A. Greibach Michael A. Harrison Ellis Horowitz Daniel J. Rosenkrantz Jeffrey D. Ullman Moshe Y. Vardi In memory of Seymour Ginsburg 1928 - 2004. 5-12 2005 34 SIGMOD Record 1 http://doi.acm.org/10.1145/1058150.1058152 db/journals/sigmod/sigmod34.html#AbiteboulHVGHHRUVH05