Youngbin Park Il Hong Suh Byung-Uk Choi Hierarchical Abstraction of World Elements and Behaviors for efficient task planning of a mobile robot. 2585-2592 2008 IROS http://dx.doi.org/10.1109/IROS.2008.4650809 conf/iros/2008 db/conf/iros/iros2008.html#ParkSC08