How do I model state?: Let me count the ways.

Ian T. Foster Savas Parastatidis Paul Watson Mark McKeown How do I model state?: Let me count the ways. 34-41 2008 51 Commun. ACM 9 http://doi.acm.org/10.1145/1378727.1378739 db/journals/cacm/cacm51.html#FosterPWM08a