Ioanna Stamatopoulou Petros Kefalas Marian Gheorghe OPERAS: A Framework for the Formal Modelling of Multi-Agent Systems and Its Application to Swarm-Based Systems. 158-174 2007 ESAW http://dx.doi.org/10.1007/978-3-540-87654-0_8 conf/esaw/2007 db/conf/esaw/esaw2007.html#StamatopoulouKG07