Franz Baader Rafael Peñaloza Boontawee Suntisrivaraporn Pinpointing in the Description Logic <i>EL</i><sup>+</sup>. 52-67 2007 conf/ki/2007 KI http://dx.doi.org/10.1007/978-3-540-74565-5_7 db/conf/ki/ki2007.html#BaaderPS07