Agent communication II : International Workshops on Agent Communication, AC 2005 and AC 2006, Utrecht, Netherlands, July 25, 2005, and Hakodate, Japan, May 9, 2006 : selected and revised papers - Dignum, Frank, 1961-; Eijk, Rogier M. van; Flores, Roberto (Roberto A.) (Lecture notes in computer science ;, 2006)