Stanislav Kurkovsky Rasiah Loganantharaj Extension of Petri Nets for Representing and Reasoning with Tasks with Imprecise Durations. 97-108 2005 23 Appl. Intell. 2 http://dx.doi.org/10.1007/s10489-005-3415-8 db/journals/apin/apin23.html#KurkovskyL05