Peter Hartel Grit Denker Mojgan Kowsari Maren Krone Hans-Dieter Ehrich Information Systems Modelling with TROLL Formal Methods at Work. 79-99 1997 22 Inf. Syst. 2/3 db/journals/is/is22.html#HartelDKKE97 http://dx.doi.org/10.1016/S0306-4379(97)00006-9