@incollection{KBBK08,
 author = {Keim, Daniel A. and Bustos, Benjamin and Berchtold, Stefan and Kriegel, Hans-Peter},
 booktitle = {Encyclopedia of GIS},
 editor = {Shekhar, Shashi and Xiong, Hui},
 publisher = {Springer},
 title = {X-tree},
 year = {2008}
}