http://doi.acm.org/10.1145/181550.181562 db/journals/sigmod/SnodgrassAABCDEGJKKKLLRSSS94.html Richard T. Snodgrass Ilsoo Ahn Gad Ariav Don S. Batory James Clifford Curtis E. Dyreson Ramez Elmasri Fabio Grandi Christian S. Jensen Wolfgang Käfer Nick Kline Krishna G. Kulkarni T. Y. Cliff Leung Nikos A. Lorentzos John F. Roddick Arie Segev Michael D. Soo Suryanarayana M. Sripada 65-86 sigmodR/23-1/P065.pdf 1994 23 SIGMOD Record 1 db/journals/sigmod/sigmod23.html#SnodgrassAABCDEGJKKKLLRSSS94 http://www.acm.org/sigmod/record/issues/9403/tsql.ps