Graham Cormode Flip Korn S. Muthukrishnan Divesh Srivastava Summarizing Two-Dimensional Data with Skyline-Based Statistical Descriptors. 42-60 2008 SSDBM http://dx.doi.org/10.1007/978-3-540-69497-7_6 conf/ssdbm/2008 db/conf/ssdbm/ssdbm2008.html#CormodeKMS08