Hector Garcia-Molina Dieter Gawlick Johannes Klein Karl Kleissner Kenneth Salem Modeling Long-Running Activities as Nested Sagas. 14-18 1991 http://sites.computer.org/debull/91MAR-CD.pdf 14 IEEE Data Eng. Bull. 1 db/journals/debu/debu14.html#Garcia-MolinaGKKS91