Verena Kantere Spiros Skiadopoulos Timos K. Sellis Storing and Indexing Spatial Data in P2P Systems. 287-300 2009 21 IEEE Trans. Knowl. Data Eng. 2 http://dx.doi.org/10.1109/TKDE.2008.139 db/journals/tkde/tkde21.html#KantereSS09