Marcello L'Abbate Ulrich Thiel Thomas Kamps Can Proactive Behavior turn Chatterbots into Conversational Agents?. 173-179 2005 conf/iat/2005 IAT http://doi.ieeecomputersociety.org/10.1109/IAT.2005.49 db/conf/iat/iat2005.html#LAbbateTK05