Yang Lu Bin Cui Jiakui Zhao Hua Lu Jialie Shen Towards Efficient and Flexible KNN Query Processing in Real-Life Road Networks. 230-237 2008 WAIM http://dx.doi.org/10.1109/WAIM.2008.10 conf/waim/2008 db/conf/waim/waim2008.html#LuCZLS08