http://doi.acm.org/10.1145/181550.181560 db/journals/sigmod/JensenCEGHJ94.html Christian S. Jensen James Clifford Ramez Elmasri Shashi K. Gadia Patrick J. Hayes Sushil Jajodia A Consensus Glossary of Temporal Database Concepts. 52-64 sigmodR/23-1/P052.pdf 1994 23 SIGMOD Record 1 db/journals/sigmod/sigmod23.html#JensenCEGHJ94 http://www.acm.org/sigmod/record/issues/9403/gloss.ps