Elias Frentzos Nikos Pelekis Irene Ntoutsi Yannis Theodoridis 151-187 2008 Mobility, Data Mining and Privacy http://dx.doi.org/10.1007/978-3-540-75177-9_7 series/springer/2008mdmp db/series/springer/mdmp2008.html#FrentzosPNT08